At least 16 people were wounded in Sunday’s attack, which took place at about 1am in a popular bar and nightlife district. Officers “put an end” to the incident quickly, Dayton police said on Twitter. The suspected shooter’s identity has not been released.

At a news conference announcing the death toll in El Paso, state governor Greg Abbott described it as “one of the most deadly days in the history of Texas”.

The Walmart attack was the eighth worst mass shooting in modern US history, after the 1984 shooting in San Ysidro that killed 21 people.

So far this year there have been 22 mass murders in the US, according to a database compiled by Associated Press, USA Today and Northeastern University that tracks killings where four or more people die – not including the offender. The 20 mass killings that preceded this weekend claimed 96 lives.

The suspected shooter in Saturday’s attack has been identified as 21-year-old Patrick Crusius from Allen, Texas, a city some 1,046km east of El Paso.

El Paso police chief Greg Allen said authorities were examining a manifesto from the suspect indicating “there is a potential nexus to a hate crime”. Officials declined to elaborate and said the investigation was continuing.

But a four-page statement posted on 8chan – an online message board often used by extremists – and believed to have been authored by the suspect, called the Walmart attack “a response to the Hispanic invasion of Texas”.

It also expressed support for the gunman who killed 51 people at two mosques in Christchurch, New Zealand.

CNN reported that the FBI has opened a domestic terror investigation into the shooting.

El Paso and Ciudad Juarez, together with the neighbouring city of Las Cruces, New Mexico, form a metropolitan border area of some 2.5 million residents constituting one of the largest bilingual, binational populations in the Western Hemisphere.

Mexico’s President Andres Manuel Lopez Obrador said three Mexican nationals had been killed and six others were wounded.

Among the dead was a 25-year-old woman who was shot while holding her two-month-old son, her sister said.

Leta Jamrowski, 19, of El Paso learned on Saturday afternoon that her sister Jordan Anchondo was among the victims. She was interviewed while waiting at the University Medical Centre of El Paso, where her nephew was being treated for broken bones – the result of his mother’s fall.

“From the baby’s injuries, they said that more than likely my sister was trying to shield him,” she said. “So when she got shot she was holding him and she fell on him, so that’s why he broke some of his bones. So he pretty much lived because she gave her life.”

Anchondo was the mother of three children.

US President Donald Trump said on Twitter that the reports from El Paso were “very bad, many killed”.

“Today’s shooting in El Paso, Texas was not only tragic, it was an act of cowardice,” he wrote in a later tweet.

“I know that I stand with everyone in this country to condemn today’s hateful act. There are no reasons or excuses that will ever justify killing innocent people.”

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University Medical Centre of El Paso received 13 patients, including one who died, hospital spokesman Ryan Mielke told CNN.

Some of the patients were in surgery while others were in a stable condition, he added.

Two of the patients who arrived at the hospital were children with non-life-threatening injuries who were transferred to El Paso Children’s Hospital, he said.

Local media said there was such an overwhelming response to an appeal by the police department for blood donations to help the wounded that long queues formed at medical centres, some of which had to tell would-be donors to come back on Sunday.

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Multiple law enforcement agencies raced to the scene at the Walmart and nearby Cielo Vista Mall, including police, state troopers, Homeland Security agents and border patrol.

Shoppers fled for their lives, including Kianna Long who was at the Walmart with her husband when they heard gunfire.

“People were panicking and running, saying that there was a shooter,” Long said.

“They were running close to the floor, people were dropping on the floor.”

Long and her husband sprinted through a stockroom at the back of the store before sheltering with other customers in a steel container in a shipping area.

Graphic video from the scene posted on social media showed what appeared to be dead bodies and wounded victims. Tales of heroism also emerged.

Walmart said in a statement: “We’re in shock over the tragic events at Cielo Vista Mall … We’re praying for the victims, the community and our associates, as well as the first responders.”

Stores at the mall were also locked down as police officers cleared the shopping centre in the east of the city, which lies on the southern US border with Mexico.

Video posted on Twitter showed customers at one department store being evacuated with their hands up.

Mass shootings are common in the United States. On Sunday, a teenage gunman opened fire with an assault-style rifle on the crowd at a food festival in Northern California, killing three people before fatally shooting himself.

At a Democratic presidential candidate forum in Las Vegas a clearly emotional Beto O’Rourke, a former Texas congressman who is from El Paso, broke the news to the audience that he had just heard about the deadly mass shooting in his home city.

O’Rourke said he had spoken to his wife Amy, who was driving in the city with one of their children. Addressing reporters, he teared up and struggled to deliver a short statement.

“I am incredibly saddened and it’s very hard to think about this,” he said.

“El Paso is the strongest place in the world. This community is going to come together. I’m going back there right now to be with my family, to be with my hometown.”

O’Rourke was among the Democratic presidential candidates who expressed outrage about the prevalence of mass shootings, blaming the National Rifle Association and its congressional allies.

“It’s not just today, it has happened several times this week. It’s happened here in Las Vegas where some lunatic killed 50 some odd people,” Vermont Senator Bernie Sanders said as he and 18 other White House hopefuls were in Nevada to address the nation’s largest public employees union.

Sanders blasted Republican Senate leadership for being “more concerned about pleasing the NRA than listening to the vast majority of the American people” and said that President Donald Trump has a responsibility to support commonsense gun safety legislation.

Earlier, O’Rourke told the forum he had heard early reports that the shooter might have had a military-style weapon, saying the country needs to keep such firearms “on the battlefield. Do not bring it into our communities.”

O’Rourke said the US may require direct action, urgency and in some cases nonviolent civil disobedience, to make real change.

“I believe in this country. I believe, at the end of the day, we’re going to be able to get this done,” he said, “but it’s going to be because of those people who force it to get done.”

Some recent deadly US mass shootings

May 31, 2019: Long-time city worker DeWayne Craddock opened fire in a building that houses Virginia Beach government offices. He killed 12 people and wounded several others before he was gunned down by police.

Feb. 15, 2019: Gary Martin killed five colleagues at a manufacturing plant in Aurora, Illinois, during a disciplinary meeting where he was fired. He wounded one other employee and five of the first police officers to arrive at the suburban Chicago plant before he was killed during a shoot-out by police.

Nov. 7, 2018: Ian David Long killed 12 people at a country music bar in Thousand Oaks, California, before taking his own life. Long was a Marine combat veteran of the war in Afghanistan.

Oct. 27, 2018: Robert Bowers is accused of opening fire at Tree of Life synagogue in Pittsburgh, Pennsylvania, during Shabbat morning services, killing 11 and injuring others. It’s the deadliest attack on Jews in the US in history.

June 28, 2018: Jarrod Ramos shot through the windows of the Capital Gazette offices in Annapolis, Maryland, before turning the weapon on employees there, killing five at The Capital newspaper. Authorities say Ramos had sent threatening letters to the newspaper before the attack.

May 18, 2018: Dimitrios Pagourtzis began shooting during an art class at Santa Fe High School in Santa Fe, Texas. The 17-year-old killed eight students and two teachers and 13 others were wounded. Explosive were found at the school and off campus.

Feb. 14, 2018: Nikolas Cruz shot and killed 17 students and staff members at Marjory Stoneman Douglas High School in Parkland, Florida. It surpassed Columbine High School as the deadliest shooting at a high school in US history.

Nov. 5, 2017: Devin Patrick Kelley, who had been discharged from the US Air Force after a conviction for domestic violence, used an AR-style firearm to shoot up a congregation at a small church in Sutherland Springs, Texas, killing more than two dozen.

Oct. 1, 2017: Stephen Paddock opened fire on an outdoor music festival on the Las Vegas Strip from the 32nd floor of a hotel-casino, killing 58 people and wounding more than 500. SWAT teams with explosives then stormed his room and found he had killed himself.

Additional reporting by Reuters and Associated Press