One person has critical injuries and a second has moderate injuries.
A Wellington Free Ambulance spokesperson confirmed they transported two people to Wellington Hospital.
Motorists were asked to detour through Newtown or to head around the bays.
Buses also experienced delays, and Wellington Airport advised customers catching a flight to plan ahead.
Police said the single-vehicle crash happened just after 6am.
A spokesperson said fire crews freed a person who was trapped in a vehicle.
The Serious Crash Unit was on site.
Meanwhile people heading south from Auckland this morning have reported heavy delays after a truck breakdown on State Highway 1 just after the Mill Rd on-ramp near the Bombay Hills.
The breakdown just after 6am had been towed clear of lanes by 8am but delays and congestion were expected.