Police want the public's help to identify the offenders of two sexual assaults in Christchurch last night.

In the first incident a 21 year old woman got into a red car at about 10 o'clock and was driven to a central city street where she was sexually assaulted.

In the second incident at about 10.15 an 18 year-old woman got into a white van believing it to be occupied by only one driver - only to realise there were two others in the back of the van.

She was driven around the central city and sexually assaulted by all three men before she was able to escape about half an hour later.

One of the vehicles has been described as a shiny, new looking red sedan, with dark coloured interior and a spoiler on the boot.

The man driving it is described as being Caucasian, approximately 30 years old with tattoos on his neck and thigh.