Ontario's police watchdog is investigating after a woman allegedly crashed her vehicle in Welland, then fell face down while "bleeding profusely" when Niagara Regional Police arrived.

In a media release, the Special Investigations Unit said police were called to a single-vehicle collision near the corner of Quaker and Rice Roads around 1 a.m. Friday.

When officers arrived, the 21-year-old woman "went to the ground face down" and officers noticed she was bleeding heavily, according to the SIU.

The woman was transported to hospital where she was declared dead.

Three SIU investigators and two forensic investigators have been assigned to the case. Anyone with information about the crash is asked to call the lead investigator at 1-800-787-8529.