China's Xiaomi said on Tuesday that it was actively cooperating with police after a fatal accident involving a SU7 electric vehicle on March 29 and that it had handed over driving and system data.

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

Xiaomi's shares, which had risen by 34.8% year to date, closed down 5.5% on Wednesday, underperforming a 0.2% gain in the Hang Seng Tech index.

“Xiaomi will not shy away, will continue to cooperate with police investigation, do our best to respond to the concerns of the family and the community“, founder Lei Jun said on Tuesday in a Weibo post.

US-listed Xiaomi ADR fell 6.2% in morning trading.