State Highway 2 has been blocked in both directions by a crash involving three cars on Moonshine Bridge in Upper Hutt.
A Transport Agency spokesperson said diversions were in place but there were significant delays and people should take the train or delay driving if they could.
The Fire Service said four people were injured in the 7.45am crash, two seriously and two moderately. One was flown to Wellington Hospital, while the other three were taken by road.
The bridge was structurally damaged in the crash, the Transport Agency spokesperson said.
