A 20-year-old male is in a serious condition after a ride on mower rolled on Waiheke Island.

The Westpac Rescue Helicopter is on its way to Oneroa, after emergency services were called to the incident at 7.27am.

A St John spokeswoman said the man fell off the tractor, and it is believed to have rolled onto him.

He has been flown to Auckland City Hospital.