Several hours after the invasion began, Hamas militants were still fighting gunbattles inside several Israeli communities in a surprising show of strength that shook the country. At least 40 people have been killed in Israel during fighting with Palestinian militants on Saturday, the Magen David Adom emergency medical services said.

“Since the morning hours, MDA teams provided medical care to hundreds of casualties, and pronounced 40 people dead,” it said, while the Israeli health ministry confirmed that at least 779 people had been injured and taken to hospitals.

Hamas, which rules Gaza and is classified as a terrorist organisation by the US, said it was the start of a major operation. The Israeli government sent warplanes to strike back within the strip.

At least 198 people in the Gaza Strip have been killed in Israel’s retaliation and at least 1,610 wounded, the Palestinian Health Ministry in Gaza said.

The Israel military confirmed prisoners of war were taken by Hamas during Saturday’s fighting, citing hostage “incidents” in Ofakim and Bari. Military spokesman Daniel Hagari said that they do not have exact numbers yet.

Also, an unknown number of Israeli soldiers and civilians had been seized and taken into Gaza.

Violence between Israel and the Palestinians has been surging for almost two years, with fatalities in the occupied West Bank hitting a scale not seen in years.

Israel is “at war. Not an operation, not a round – war”, Prime Minister Benjamin Netanyahu said in a video statement after what he termed a “lethal, surprise offensive” by Hamas early Saturday.

Netanyahu said he had issued guidance to the heads of Israel’s security establishment to “cleanse all settlements of the terrorists who have infiltrated them”. Israel’s reserves will be mobilised to “fight back at a scope and power that the enemy has not met”, he added.

Israel’s Defence Minister Yoav Gallant said Palestinian militant group Hamas has “launched a war against the State of Israel”.

“Troops are fighting against the enemy at every location,” he said in a statement.

AFP journalists said Israel’s military began air strikes on Gaza, following the rocket barrage from inside the territory which is sealed off from Israel by a militarised border barrier.

“Dozens of IDF fighter jets are currently striking a number of targets belonging to the Hamas terrorist organisation in the Gaza Strip,” the military said.

Rockets had earlier streamed across the sky repeatedly after the first launches from multiple locations across the Palestinian territory from 6.30am (03:30 GMT), AFP journalists in Gaza City reported.

The armed wing of Hamas said it was behind the aerial assault, saying its militants had launched more than 5,000 rockets and its fighters seized an Israeli tank.

“We decided to put an end to all the crimes of the occupation (Israel), their time for rampaging without being held accountable is over,” the Ezzedine al-Qassam Brigades said.

“We announce Operation Al-Aqsa Flood and we fired, in the first strike of 20 minutes, more than 5,000 rockets.”

Israel’s army did not immediately comment on the tank claim when contacted by AFP.

Air raid sirens wailed across Israel’s south and central areas, with the Israeli army urging the public to stay near bomb shelters.

AFP journalists in Jerusalem heard multiple rockets being intercepted, with sirens blaring across the city on more occasions than in any Gaza conflict in the past three years.

Hundreds of residents fled their homes in eastern Gaza to move away from the border with Israel.

Men, women and children were seen carrying blankets and food items as they left their homes, mostly in the northeastern part of the Palestinian territory.

Hamas “will face the consequences and responsibility for these events”, Israel’s military said in a statement.

A woman in her 60s was killed “due to a direct hit” in Israel, the Magen David Adom emergency services said.

Fifteen others were wounded, two of them seriously, doctors said.

In a statement posted on Telegram, Hamas called on “the resistance fighters in the West Bank” as well as “our Arab and Islamic nations” to join the battle.

Israel’s army said it was fighting Gaza militants who entered Israel by land, sea and air using paragliders on Saturday.

“It was a combined ground raid which happened through paragliders, through the sea and through the ground,” army spokesman Richard Hecht said.

“Right now we’re fighting. We’re fighting in certain locations around the Gaza Strip... our forces are now fighting on the ground” in Israel, he added.

Hecht confirmed there were casualties but would not be drawn on details, nor discuss reports that multiple Israelis had been captured by Palestinian militants.

Thousands of military reservists are set to be drawn up for Gaza, as well as northern Israel, near foes Lebanon and Syria, and the occupied West Bank.

“We’re looking at all arenas... we understand this is something big,” Hecht said.

Israel has imposed a crippling blockade on Gaza since 2007 after the Hamas militant group took power.

Palestinian militants and Israel have fought several devastating wars since.

The latest fire follows a period of heightened tensions in September, when Israel closed the border to Gazan workers for two weeks.

The shutdown of the crossing came as Palestinian protest rocked the heavily-militarised border.

02:29

‘Don’t be afraid, Dad is coming’: Gaza children awakened by explosions amid Israeli air strikes

‘Don’t be afraid, Dad is coming’: Gaza children awakened by explosions amid Israeli air strikes

Protesters had resorted to burning tyres and throwing rocks and petrol bombs at Israeli troops, who have responded with tear gas and live bullets.

Critics had slammed the border closure as collective punishment against thousands of Palestinian workers, who have far greater earning potential in Israel than Gaza, where unemployment is rife.

Resuming their passage on September 28 had raised hopes of calming the situation in Gaza, home to 2.3 million people.

In May, an exchange of Israeli air strikes and Gaza rocket fire resulted in the deaths of 34 Palestinians and one Israeli.

So far this year, at least 247 Palestinians, 32 Israelis and two foreigners have been killed in the conflict, including combatants and civilians on both sides, according to Israeli and Palestinian officials.

The vast majority of fatalities have occurred in the West Bank, which has been occupied by Israel since the 1967 Arab-Israeli conflict.

There has been a rise in army raids, Palestinian attacks targeting Israelis and Israeli settler violence against Palestinians and their property.

Several far-right Israeli ministers live in settlements in the West Bank, which are deemed illegal under international law.