A man has been airlifted to hospital after being attacked by a bull north of Auckland this morning.

The Auckland Westpac Rescue Helicopter was sent to Dairy Flat about 8.30am to treat the man, aged in his 40s.

A spokeswoman for the rescue service said the man was working when the bull "gored him" in the leg.

He was transported to Auckland City Hospital in a serious condition, she said.