Passenger describes shock at seeing smoke enter lower cabin of commuter vessel en route to Whangaparaoa.
Smoke billowed into the lower deck of a commuter ferry last night from a faulty engine, sparking a mayday call and emergency action.
A passenger on the 360 Discovery ferry said her stomach dropped when she saw what she thought was smoke rise from the floorboards.
"It made your heart skip a beat," said Gulf Harbour resident Kris Wetherill.
"It wasn't exactly terrifying, but it was definitely an uneasy feeling."
The 5.25pm service departed Auckland for Whangaparaoa on schedule but ran into trouble about halfway through its trip.
Emergency services were alerted at 6.08pm to what was initially suspected to be an on-board fire.
Three firefighting teams were dispatched and a naval vessel was sent to the ferry's assistance. A police launch, three coastguard boats and a helicopter soon followed.
On the ferry, the three crew quickly ordered the 57 passengers to their emergency muster points.
"I knew that everybody needed to keep cool, and I think everybody knew that," Ms Wetherill said.
Within three minutes, passengers were getting updates, she said, and the passengers in the lower deck had been moved upstairs.
The ferry's crew shut down one of the two engines, which had been overheating.
With the navy's HMNZS Manawanui and police launch Deodar - carrying ambulance and fire crews - at its side, the ferry was able to continue its run to Whangaparaoa.
It arrived about 6.45pm, said a ferry spokeswoman, or about 20 minutes late. Two fire service teams met the disembarking passengers at Gulf Harbour. Nobody had been injured.
Shayne Kennedy, the deputy chief fire officer at the scene, said it appeared the engine had overheated, much like a car engine but on a bigger scale.
"There was a lot of smoke and a lot of heat. There was potentially a fire danger [there], so obviously the skipper did the right thing," he said.
A fire investigation crew took an initial look around the ferry after it arrived. The ferry spokeswoman, Lucy Farrington, said inquiries would continue.
"We can't speculate on the exact cause but tomorrow we will have a full internal investigation."
It was unclear when the vessel would be back in service.
This morning, bus replacements would be supplied for commuters who showed up at the wharf - but this had been planned for today anyway due to bad weather, Ms Farrington said.
"We will think about how we will follow up with the passengers tomorrow. Obviously an apology.
"We're just glad they're safe - [their safety] was our priority."
The 17-metre ferry had reported a fire in its engine room one nautical mile east of Campbell's Bay on Auckland's North Shore, said a Coastguard report.
But Ms Farrington said reports of fire had been a mistake.
"It was a small mechanical issue, and there was steam coming off the engine."