The explosion took place this evening at the exit of the south railway station of Urumqi. Ambulances and police cars rushed to the scene, state-run Xinhua news agency reported.
The blast came just as President Xi was wrapping up a tour of insurgency-hit Xinjiang province in which he spoke of plans to get tough on fighting terrorism.
Scores of people have been injured, reports said.
Police have cordoned off all entrances to the square of the station. Armed police have been deployed in the square. Train services had been suspended at the station, it said.
Resource rich Xinjiang has witnessed a spurt in attacks by Islamic militants in recent years as province experienced ethnic tensions between native Uygur Muslims and Han Chinese settlers from other provinces.
Xi visited an armed police team in Kashgar, the border town close to Pakistan-occupied Kashmir, on Sunday where he acknowledged the complicated situation and the hardship the soldiers have endured.
Thirty three people were killed 143 injured in knife attacks by a group of militants on passengers at Kunming Railway station on March 1.
