One third of young gay men have never been tested for HIV or other sexually transmitted infections despite the fact that they are increasingly likely to have unprotected sex with casual partners.

Health professionals have raised concerns about the 65 per cent increase in the number of men aged 18-24 newly diagnosed with HIV in NSW between 2009-12.

Medical bodies and community groups have responded by taking testing to the streets in a bid to encourage more young men to find out their HIV status.

There are 19 sites in NSW offering rapid HIV testing, in which people who give a finger prick of blood can get a result in 30 minutes.

Staff working out of a retro caravan in Newtown will be encouraging evening commuters to take the test this week in the lead-up to the annual Mardi Gras parade on Saturday. The public health push comes on the heels of new findings by the Centre for Social Research in Health at UNSW which revealed that 32 per cent of gay men aged between 16-26 years have never been tested for HIV or other STIs, compared with 5.6 per cent of their older counterparts.