A ferry driver is being investigated over an incident that left a passenger trailing in the water behind the boat.

Carl Saunders was walking onto a ferry from Waiheke Island to Auckland with his four-year-old son Kiel last Tuesday night when the gangway broke.

The boat then surged forward leaving him hanging over the water. 

Maritime New Zealand has spoken to the driver who accidentally put the boat in gear, causing it to surge forward and break the gangway.

It was too early to say whether any charges would be laid, Maritime NZ spokesman Steve Rendell said.

He said everyone involved was being spoken to in the hope lessons could be learned from the incident.

Ferry operator Fullers is also investigating the incident.

It's the second ferry-related incident in two days in Auckland waters.

Last Monday evening, smoke was discovered coming from the engine of a 360 Discovery ferry while 57 passengers were onboard.

An overheated engine sparked the smoke, which was discovered by smoke detection systems.

People were evacuated to the deck and a mayday call was issued at 6pm. The Auckland to Gulf Harbour ferry was escorted to its destination shortly afterwards.

Fullers and Maritime NZ are investigating.

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- © Fairfax NZ News