Three separate bus explosions killed at least three people and injured 14 in the south-western Chinese city of Kunming media said.

The explosions occurred within 55 minutes of each other during the peak morning rush hour in downtown Kunming, the capital of Yunnan province, Xinhua reported, citing local police.

The cause of the explosion was under investigation, the report said. Kunming police declined to comment.

Photos of one of the damaged buses that were posted on the Yunnan Daily website showed the vehicle's windows blown out by the blast and shattered glass on the road.

The first explosion occurred at 7.10am (local time) near a bus stop in a central part of the city, and the second blast was at a nearby intersection of two roads at 8.05am, Xinhua reported.

- AFP