The B.C. Civil Liberties Association is demanding an explanation from the Vancouver Police Department after a surveillance video showed an officer pushing a disabled woman to the ground.

The video was taken at the beginning of the month on the sidewalk on Hastings Street, near the crowded United We Can recycling centre.

The woman, who has cerebral palsy, appears to brush an officer who is walking with two others.

The officer shoves the woman to the ground and the three stand over her before walking away, leaving her lying on the ground.

There is no sound on the video, so it's not known if the woman threatened the officers, but David Eby of the Civil Liberties Association says there appears to have been no reason for the shove.

"We imagine she would be hauled off and handcuffed if she said something threatening to the officers. It's clear that they didn't see grounds for arrest, but even if they did it is hard to imagine that the force that they used was appropriate.

"She looks like she weighs about 90 pounds in the video. She is clearly disabled," Eby said. "There was no need for any use of force."

Eby said such an incident wouldn't happen in Kerrisdale or Point Grey and it shouldn't happen in the Downtown Eastside.

The professional standards section of the Vancouver Police Department is investigating.

At a news conference Thursday afternoon, Const. Jana McGuinness said the officer has been on the force for little more than a year and is still out on patrol.

She said the officer reported the incident to his supervisor immediately, a move which initiated an investigation.

"Many of the answers are going to come from the investigation and we need to allow it to run its course. We recognize that those who view this video are going to find it unsettling and concerning," she said.

McGuinness said the officer apologized to the woman a short time after the incident, expressing regret for his action and for not helping her up.