Firefighters and two helicopters are battling a serious bush fire threatening three or four homes on Auckland's North Shore. 

Fire and Emergency were alerted to a fire in trees and thick bush near Okura River Rd about 2.20pm today. 

Colin Underdown, shift manager for Northern communications, said about 30 to 40 staff are battling the fire that threatens three or four homes on East Coast Rd. 

He said two helicopters, four water tankers and six fire engines are at the scene. 

The fire is being fuelled by an easterly wind and covers about 5ha, Underdown said. 

He did not know how close the fire is to the homes and whether the residents, who alerted Fire and Emergency, had left their homes.