Traffic is backed up on Auckland's northwestern motorway after a van hit a barrier, blocking a lane.

The incident occurred between the Lincoln Rd and Royal Rd off ramps on SH16 shortly before 6pm.

Two people have been seriously injured in the crash and seven people have minor injuries, a police spokeswoman said.

Traffic is backed up on Auckland's Northwestern Motorway. Photo / NZME

A white van has been put on a tow truck and there is a fire truck at the scene also.

Traffic is slowly starting to move again. However, the stretch of motorway resembled a carpark as traffic was at a complete standstill for some time.

Some people had stepped out of their vehicles and were sitting on car bonnets. Others near the Royal Rd onramp were standing on top of their vehicles trying to see what was causing the delay up ahead.

The van was on fire for a time, however no one was in the car when it was on fire, a police spokeswoman said.

A van is loaded onto the back of a tow truck on the northwestern motorway. Photo / Jason Oxenham

The road was completely blocked eastbound toward the city and one lane is now open.

A tow truck has been requested and traffic is backing up from the scene back toward Hobsonville.

Traffic was slowly starting to move again shortly before 6.30pm.

People - a number of adults - who appeared to be involved in the accident or connected to the white van on the tow truck were helped across to the side of the road by authorities.