State Highway 1 Foxton in Horowhenua is now open after it was closed by a possible gas leak.
The Fire Service said contractors dug through a high pressure gas main on the site of a former petrol station.
Fire officers from Foxton and Palmerston North are at the scene, to try and stop the gas vapour spreading.
Police said the issue had now been resolved, and the road was open again.
Motorists are asked to avoid the area if possible as delays are expected.