Traffic is becoming congested around the scene of yesterday's truck crash near Pukerua Bay north of Wellington, the Transport Agency says.
Both lanes along State Highway 1 are open at the crash site but the speed limit in the area has been reduced while repairs are carried out on the road.
NZTA spokesperson Mark Owen said there are still large numbers of motorists heading out of Wellington, causing delays throughout the Kāpiti Coast.
"Fairly busy north through Ōtaki ... there's a lot of people out on the road and we just ask them to take that extra care and plan their journies and allow plenty of space between them and the next vehicle and we want everyone to get to their destinations safely."
The Greater Wellington Regional Council has been unable to confirm yet whether hazardous chemicals from the truck have spilled into a local wetland which is home to threatened wildlife.
QEII National Trust chief executive Mike Jebson said if chemicals did reach the Taupō swamp, it would be disastrous to the ecosystem.
"The thing about these wetlands is there's so few of them left in the country, we're down to less than 10 percent of the wetlands that used to be here, so every wetland's important but Taupō swamp is particularly important."