Investigations are underway into a large fire which has damaged the sand dunes on Mount Main Beach.

Twelve firefighters attended the fire at 12:10am, the fire was about 100 metres by 50 metres.

Fire and Emergency New Zealand northern communications shift manager Mau Barbara say the crews had trouble gaining access at first.

'They had difficulty gaining access but they did find access off Oceanbeach road.

'It was brought under control pretty quickly, it took about 40 minutes.”

He says there were three appliances in attendance, two from Mount Maunganui and one from Tauranga station.

Fire crews left the scene around 1.20am.

The cause of the fire is unknown at this stage.