Northbound traffic on Auckland's Southern Motorway is crawling from Highbrook to the city due to a crash at Spaghetti Junction this afternoon.

The NZ Transport Agency says debris from the crash has been cleared and two northbound lanes are now open, but traffic is still congested from Highbrook.

"Delay your journey, allow extra time or consider alternate route," it advised motorists on Twitter at 4.20pm.

It posted video at 3.50pm showing northbound traffic banked up to Ōtāhuhu.