Investigations are underway into the cause of a crash where a vehicle careered down a 25m bank.

Emergency services, including the Thames Volunteer Fire Brigade and the Auckland Westpac Rescue Helicopter, were called to the crash in the Kaueranga Valley just before 5.30pm on Sunday.

"On arrival, we discovered five, very lucky, occupants of the vehicle that had careered down a 25 metre bank had extricated themselves from the upside down, submerged car with the assistance of some locals," says a post on the Thames Volunteer Fire Brigade Facebook page.

"We assisted St John with first aid on all patients, and set up a landing zone for the Westpac helicopter crew, before they winched three of the five patients somewhere more easily accessible for the ambulance crew to treat them."

A spokesperson for the rescue helicopter says all of the people were reported to be in moderate condition.

"They were left in the care of road ambulance crew and Westpac 1 returned to base."