Contractors will work throughout the night to remove fuel from a crashed petrol tanker on State Highway 57 in Shannon.
The crash on the small Horowhenua town's main street caused power cuts and prompted a warning for residents to stay inside.
The tanker rolled about 4pm on Monday, leaking fuel onto Plimmer Terrace.
Police say another tanker is at the scene late on Monday night to pump fuel out of the overturned tanker which is being kept stable by a crane.
The regional council has been cleaning up the fuel and police say while the stench of fumes has subsided, people should remain indoors as a precaution.
Sergeant Andy Dow says removing the fuel is going to be a slow job, as six compartments need to be drilled into and decanted. He estimates this should be completed about 4.30am on Tuesday.
Police say cordons and diversions will stay in place until the scene has been cleared.
Power has been cut to much of Shannon because of the threat of the fuel sparking a fire. Lines company Electra says power should be restored by midnight at the latest.
The incident also closed part of the adjacent railway line and disrupted some services.
KiwiRail says the Northern Explorer from Auckland to Wellington was stopped at Palmerston North and passengers were put on a bus service to the capital.
A bus service replaced the Capital Connection service from Levin to Palmerston North.
There have been some minor delays for freight services.