Xinjiang authorities said two assailants carried out a suicide attack on Wednesday evening at Urumqi's main railway station. The attack left one bystander dead and 79 people injured.
The assailants, one of whom was identified as Sedirdin Sawut, 39, from Aksu in southern Xinjiang, were influenced by "extreme" religious thoughts, Xinhua reported.
The assailants "set off bombs tied on their bodies and died" after launching frenzied knife attacks, People's Daily reported through its official microblog, citing a police investigation.
"This is a bomb explosion case of a violent terrorist nature," Xinhua reported, but it did not say whether the attackers were related to overseas groups.
The regional government did not say if police had detained any people. An overseas Uygur group said up to 100 had been arrested.
Security and Xinjiang affairs experts said the incident was planned as Xi wrapped up his visit - a sign that extremists were escalating confrontation with the leadership in Beijing.
Yesterday armoured vehicles were stationed at the entrances of the railway station, with hundreds of armed officers with riot shields patrolling nearby. The station exit, where the blast took place was cordoned off.
"We were waiting outside the station for a train, and then the bomb exploded. Many pieces of luggage were scattered around. I then saw a man whose leg was seriously hurt limping out of the station," said a traveller from Wuxi in Jiangsu province, who was hoping to get on a train to Ili prefecture in northern Xinjiang on Wednesday night. It was cancelled.
"Some people were chopping others with their knives, and then came the sound of the explosion, which was deafening," said the shopkeeper of a nearby mobile phone accessories shop.
Security in other Xinjiang cities was stepped up. Police in Yining posted a notice calling on local residents to report to authorities on people suspected of keeping explosives and guns, China News Service reported.
President Xi urged "decisive action" against violent terrorist attacks after the blast.
"The battle to combat violence and terrorism will not allow even a moment of slackness, and decisive action must be taken to resolutely suppress the terrorists' rampant momentum," Xinhua quoted Xi as saying.
Rohan Gunaratna of the Singapore-based International Centre for Political Violence and Terrorism Research, said: "The attack is a defiance of [Beijing's] rule. They want to show to the Chinese president that they are able to attack."
Li Lifan, a professor of Central Asian studies at the Shanghai Academy of Social Sciences, said the assailants were seeking "more attention from the international community for their cause".
Given Wednesday's attack and the knife attack at the Kunming railway station in March, which left 33 people, including four attackers, dead, experts called on authorities to be more vigilant about the spread of violence from southern Xinjiang to other regions.
"Attacking during Xi's visit and the use of bombs that also could have killed Uygur [bystanders] indicates that the assailants are getting indiscriminate in their targets," said Pan Zhiping , who formerly worked for the Xinjiang Academy of Social Sciences.
Rafaello Pantucci, a senior research fellow with the London-based Royal United Services Institute, said the incident was a "substantial security failure" by the Xinjiang government as it could not prevent an attack even during a visit by top state leaders."We are seeing the problem getting worse and slowly spreading out to all over the place," he said.
Dilxat Raxit, spokesman for the World Uygur Congress, said Uygurs expected Xi to give suggestions to improve their situation during the visit. He said Wednesday's attack was a result of Beijing's suppression.