A man has been airlifted to hospital after hurting his back sliding down sand dunes at a West Auckland beach today.

The man, believed to be aged in his 20s, was flown to Auckland City Hospital from Lake Wainamu near Bethells Beach at 6.30pm.

Auckland Rescue Helicopter Trust pilot Alan Deal said the man was transported in a moderate condition with back injuries.

"He had been sand surfing down the sand dunes and he'd taken a bit of a tumble," Mr Deal said.

"It's a pretty steep slope."

The sand dunes are 30m to 40m high and a popular attraction in the area.

Members of Bethells Beach Surf Life Saving Club assisted with first aid for the man and secured a landing site for the helicopter.