VANCOUVER - A Vancouver woman was taken to hospital in serious condition after being stunned with a Taser during a confrontation with city police.

Const. Jana McGuinness of the Vancouver Police Department said the incident occurred on the city's Downtown Eastside on Tuesday morning.

The woman suffered a head injury falling to the ground after being shocked by police during the incident.

"Police encountered a distraught woman on the sidewalk ... waving a large folding knife," McGuinness said in a media release.

"Early information indicates that police repeatedly told the woman to drop the knife while they redirected pedestrian traffic away from her."

McGuinness said the woman yelled obscenities at the officers and challenged them to shoot her.

"She held the knife in an aggressive stance as she came at the officers," McGuinness said.

Police said an officer drew a Taser but did not fire, instead moving back to a safe distance.

The standoff continued until a man in the crowd ignored commands from police and ran up to the woman.

He grabbed at the woman's arm to try and get her to release the knife but was unable to do so.

"Police fearing for the man's safety fired the Taser. The woman fell to the ground, hitting her head but still clutching the knife," McGuinness said.

The department's major crimes unit is investigating and the provincial office of the police complaint commissioner has been notified of the incident.