China's President Xi Jinping has ordered troops in Xinjiang to deliver a "crushing blow" to terrorism, state media reported on Thursday after a bomb attack in the regional capital killed three people and injured 79.

The blast at the Urumqi South railway station came as Xi wrapped up a high-profile, four-day visit to the region that had focused on targeting extremism. It was the third major incident in seven months targeting civilians, following earlier fatal attacks in the heart of Beijing and Kunming in south-western China.

The north-western region has seen repeated outbreaks of violence, which authorities blame on separatist terrorists but human rights groups and analysts say have been fuelled by grievances of the Muslim Uighur population at Beijing's policies. Many chafe at religious and cultural restrictions, economic disparities and Han Chinese migration into the region, which they say have eroded their way of life.

State media said Wednesday's blast took place just after 7pm, shortly after a train pulled in, hitting travellers as they streamed from a station exit. Initial reports suggested that attackers had also slashed at people with knives.

The state news agency Xinhua quoted police as saying two of the dead were suspected of the attack and had "long been involved in religious extremism". It named one as Sedirdin Sawut, a 39-year-old man from Xayar county, Aksu, in southern Xinjiang.

The third fatality was described as an innocent civilian. Four of the wounded have serious injuries but are stable, Xinhua added.

The official People's Daily newspaper's microblog said that the attackers had strapped bombs to their bodies. Experts warned that with details of the attack still unclear it was too early to say whether it was a suicide bombing.

A vendor told Xinhua he thought there had been an earthquake because the explosion was so powerful, while a 57-year-old survivor told the Associated Press that the blast had knocked her to the ground.

"I saw I had shreds of flesh and blood in my hair and on my clothes. It was terrifying," said the woman, who would only give her surname, Peng.

Following the blast, the president declared: "The battle to combat violence and terrorism will not allow even a moment of slackness, and decisive actions must be taken to resolutely suppress the terrorists' rampant momentum."

In earlier comments from his trip, not reported until after the attack, Xi said China would deal a crushing blow to terrorists and deploy a "strike-first" strategy.

He told officials that the long-term stability of Xinjiang was vital to the whole country's development and its "unity, ethnic harmony and national security".

Earlier last month several Chinese cities announced they were putting armed officers on patrol. Those measures came after knife-wielding assailants killed 29 civilians and injured 143 more at a railway station in south-western Kunming in March. In October, a car ploughed into crowds in Tiananmen Square in Beijing, killing the three occupants and two bystanders. Authorities blamed that attack too on separatists.

A Xinhua article warned on Thursday: "Separatists appear to be shifting their focus from symbols of the government – such as public security stations and police vehicles – to random, ordinary civilians, and operating in areas outside Xinjiang."

Philip Potter, an expert on terrorism in China at the University of Michigan, said that a suicide bombing, if proved, would be a notable escalation.

He added: "We are seeing a number of things that suggest there is a lot of capability on the side of the militants. I don't necessarily mean a large, dark, secret organisation; I don't necessarily mean it's co-ordinated.

"It means that there is pent-up capability within the broader population. The fact you can execute an attack at a symbolically valuable moment means in some way you are holding capability in reserve."

All of the three recent attacks were "much harder than jumping in the back of a pick-up truck in Khotan and stabbing police [as in previous incidents]," he noted.

Potter added that he did not see evidence of operational ties with foreign groups, but warned of the potential dangers if Uighur fighters who were involved with jihadist groups abroad came home. "The grievances are entirely about domestic Uighur disgruntlement in China. The question is whether there are circumstances in which the international situation throws fuel on the fire," he said.

James Leibold, an expert on ethnicity in China at Melbourne's La Trobe University, said the Urumqi attack was a clear sign that some Uighurs felt marginalised and sought to "explicitly revoke participation within Xi Jinping's 'China dream'."

He said that Xi and the party-state had "doubled-down on Xinjiang over the last year ... seeking to penetrate the party-state deeper into the lives of ordinary Uighurs" through multiple measures including a "mass-line campaign" which has seen 70,000 officials sent to work in villages, intensified bilingual education and a deepening of economic reforms, as well as more pervasive public security.

Leibold added: "Any potential spike in inter-ethnic violence does not pose a direct threat to Xi Jinping and party-state rule in China, but there is an increasing concern that the party-state's ethnic policies have failed ... Xi Jinping can ill afford to look soft, weak or unresponsive to the perception that Xinjiang and the Uighurs might soil or reject the China dream."