A vehicle which police say is "possibly a caravan" has overturned on State Highway 2, in the Waikato region, and is causing lengthy delays for travellers.

The vehicle crashed around 4.45 this afternoon on SH2 near Mangatawhiri.

When police officers arrived the vehicle, which was "possible a caravan" was on its side.

"It doesn't appear there are any injuries however the westbound lane is blocked," police said in a statement.

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According to the NZ Transport Agency, all westbound lanes were blocked and there were significant delays.

Traffic control measures were in place.