Three helicopters and twelve fire crews are battling a large scrub fire in Hawke's Bay.

The fire was initially 400 square metres in size, but has now stretched to four hectares and has reached a five-year-old pine plantation, making it extremely difficult for ground crews to access.

Waka Kotahi – New Zealand Transport Agency – has closed the Napier-Taupō Road on State Highway 5 with no detours available to travellers.

Hawke's Bay Fire and Emergency area commander Ken Cooper says firefighters had received ‘'multiple'' calls after the fire broke near the Te Hāroto district, near Tataraakina Road, about 12pm on Thursday.

Ken says firefighters were facing 'challenging” conditions and the highway had been closed for safety reasons – mainly as helicopters were flying over the road.

He says the flames are nowhere near the highway.

Hawke's Bay was experiencing extreme fire danger levels due to high temperatures and strong winds.

No houses were at risk, Ken says.

It's the 12th vegetation fire Hawke's Bay crews have been called to in the past week.

On Wednesday, a helicopter, an urban tanker and three rural fire units extinguished a 300m long grass fire on Crownthorpe Settlement Rd near Hastings.

A Fire and Emergency spokesperson says the fire was contained and extinguished in minutes.

Hawke's Bay fire crews earlier warned of increasing fire risk after attending 10 vegetation fires during the past week alone.

The fires were caused by people burning un-permitted fires, power lines sagging onto trees due to the heat and one fire was an old burn that had been burning underground since it had been buried last year.

-Stuff