Three people were killed and 79 others injured in an attack on a railway station in China's Xinjiang late Wednesday, state media said, as the president wrapped up a trip to the restive region.

China's official news agency Xinhua said attackers slashed people with knives and set off explosives at the south railway station in Xinjiang's capital Urumqi, calling it a "violent terrorist attack".

The assault came on the same day that President Xi Jinping ended a visit to Xinjiang in China's far west, home to the country's mostly Muslim Uighur minority.

The vast and nominally autonomous region of Xinjiang, where Uighurs are the largest ethnic group, is periodically hit by deadly clashes that authorities blame on terrorists but which rights groups say are driven by cultural repression.

Four people were seriously injured in the attack but were "in a stable condition" after being sent to hospital for treatment, Xinhua reported, citing local Communist Party officials.

President Xi moved swiftly to urge "'decisive actions' against violent terrorist attacks" following the incident, Xinhua said.

"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," the news agency quoted Xi as saying.

The blast, which occurred at 7.10pm local time, was "centred around luggage left on the ground between the station exit and a public bus stop," Xinhua said, citing witnesses.

The station was closed after the incident and services suspended but it has since been reopened. Police evacuated people from nearby areas, the state news agency quoted an officer as saying.

Many online postings relating to the incident on China's Twitter-like microblog Weibo have since been removed, including images from apparent witnesses and posts from news organisations.

The attack comes weeks after 29 people were killed and 143 injured in a brutal stabbing spree at a railway station in Kunming, in southwest Yunnan province, which Beijing blamed on separatists from Xinjiang.

Four surviving members of what Beijing called a "terrorist gang" have been charged with carrying out the March attack, dubbed "China's 9/11" by state media, and are expected to receive the death penalty.

Xi, during a visit to Xinjiang which ended Wednesday, called for tougher law enforcement but also for stepped-up assimilation of minorities.

While fighting terrorism, China will deploy a "strike-first" strategy against terrorists in the region to deter enemies and inspire people, Xinhua quoted him as saying.

But he added that Beijing would implement "appropriate policies to improve ethnic harmony and common prosperity of all ethnic groups".