Police have released surveillance images of a suspect accused of sexually assaulting a female bus driver in East Vancouver last month.

The driver was groped while driving the 22 Knight Street bus south on Clark Drive near Broadway on Jan. 1, spurring the Canadian Auto Workers Union to offer a $2,000 reward for information in the case.

Const. Lindsey Houghton said the images made public Wednesday were taken moments after the assault at around 7 a.m., and depict the suspect making a "shushing" gesture.

The suspect, believed to be 22 or 23-years-old, boarded the bus at Pender and Abbott streets in downtown Vancouver.

He is described as 5-6 or 5-7 tall, between 165 and 175 lbs. with a light brown complexion. At the time of the assault he had a moustache and possibly a goatee and short, dark, parted hair.

He was well-dressed and clean in appearance, wearing dark pants and a dark-coloured pea coat over a blazer and shirt.

The union says there have been four sex assaults on female drivers since 2009. Of the 3,600 bus drivers employed by Coast Mountain Bus Company, about 12 per cent are women.

Anyone with information is asked to call the Vancouver Police Sex Crimes Unit at 604-717-2589 or Crime Stoppers at 1-800-222-TIPS.