A Wellington Metlink bus has caught fire blocking a lane of traffic on State Highway 1 this afternoon.

Four fire trucks and a water tanker are at the scene on the motorway in Linden between Tawa and Porirua.

A Fire and Emergency spokeswoman told the Herald the fire was out but crews had stayed to give the bus a “good water down”.

The NZ Transport Agency said fire blocked one of the two southbound lanes between the Mungavin Interchange and the SH1/SH59 merge.

Metlink is the Wellington region's public transport provider. Photo / Ross Setford

Metlink confirmed the bus had no passengers and was not in service.

Staff onboard the bus were safe, a Metlink spokeswoman said.

A photo posted by the agency shows a thick cloud of white smoke coming from behind an overbridge.

Police are controlling traffic.

A local posted on a community Facebook page to warn of the disruption.

“We just drove past a small Metlink bus fully ablaze between Porirua and Tawa (Southbound) on SH1 - avoid the area if you can!” the post said.

It comes after an Auckland Transport bus caught fire on the city’s North Shore this morning.

The bus driver and another person were hurriedly trying to fight the blaze with fire extinguishers while they waited for firefighters.

Auckland Transport said an out-of-service bus with no passengers on board caught fire outside the Birkenhead depot at 8.48am.

“Staff noticed smoke coming from the engine of the diesel-powered bus, and a crew from Fire and Emergency acted quickly to extinguish it.”

There were no injuries, and the cause of the fire would be investigated, AT said.