The province's police watchdog is investigating after a police chase ended in a crash on a downtown  bridge, seriously injuring a 24-year-old woman.

According to the Special Investigations Unit (SIU), Toronto police officers spotted a vehicle of interest on Sherbourne Street at around 3 a.m.

Officers followed the vehicle along Bloor and attempted to stop it, but the driver would not stop, the SIU said in a release.

Then at Parliament and Bloor streets, the vehicle left the roadway and crashed into a bridge.

A 24-year-old woman who was inside the vehicle was transported from the scene to a trauma centre to be treated for a serious injury.

Neither police nor the SIU have said why the vehicle was being pursued.

crash, bridge,

The SIU has now assigned three investigators and two forensic investigators to the case.

The SIU is an arm’s length agency that is called in to investigate any incident involving police and a member of the public that results in death, serious injury, or an allegation of sexual assault.

Bloor Street is closed in both directions between Sherbourne Street and Castle Frank Road for the investigation.