The founder of Chinese electric vehicle maker Xiaomi opens new tab said on Tuesday he was "heavy-hearted" after three people were killed in an accident involving one of the company's SU7s, and said it would fully cooperate with a police investigation.

The incident on March 29 marks the first major accident involving the SU7 sedan, which Xiaomi launched in March last year and which since December has outsold Tesla's Model 3 on a monthly basis.

In a late-night statement on his Weibo account, nine hours after an earlier company response to the accident, Lei Jun said that "at this point, I feel that I should not wait any longer, I must stand up and promise on behalf of Xiaomi: no matter what happens, Xiaomi will not evade."

Lei vowed the company would do its best to "respond to the concerns of families and society".

A disclosure from the company earlier on Tuesday said initial information showed the car was in the Navigate on Autopilot intelligent-assisted driving mode before the accident and was moving at 116 kph (72 mph).

In a rundown of the data submitted to local police posted on a company Weibo account, Xiaomi said the autopilot system had issued a risk warning of obstacles ahead.