Two trailers carrying containers have gone through the railing of a Bluebridge ferry in Wellington during rough weather.
The passenger ferry was heading into the capital from Picton around 10:30am on Monday when the b-train fell overboard.
Bluebridge commercial manager Ed Menzies said the unit was storm-lashed, and it is unclear why it moved and broke the ship's railing.
Mr Menzies says the trailer unit was carrying chilled pork and was lost overboard in the Cook Strait. It was the first time such an incident had happened for the company.
A photo taken by passenger Cesar Koene shows the affected area on the Straitsman ferry has been roped off.
One passenger, who witnessed the incident, told Newshub of their experience.
"I saw two containers spill over," they said. "They tried to grab it but it wasn't quite strong enough - it almost pulled us in. It was hardcore."
Another passenger said the boat was "going crazy" before the b-train fell off the ferry.
"Kids were holding on for dear life, screaming - I was holding on," they said.
"Then you could hear the chain snapping and people yelling out - I actually thought someone fell overboard because people were screaming.
"And then I look out and people had their phones out. I ran over 'cause the boat had levelled out by then, and I just saw the end of the truck going into the water."
The patron said the ferry felt as though "it was vertical" at the moment the trailers fell off.
A third patron was in the bathroom suffering from nausea when he first heard what had happened.
"It had been pretty full on seasickness for the previous hour and a half, and then these three waves just hit in succession and you're getting knocked around in the cabin," he said.
"Then this woman walks in, calling out to her husband, 'George, George can you come out?' and he goes, 'What are you talking about woman?' and she goes, 'A truck's just falling off the side' and he goes, 'You're bloody joking'."
Another Bluebridge traveller said they were standing with their daughters right at the very rear of the ferry when the incident occurred.
"We saw the boat going from left to right, and when it went we heard the chain snap and then we saw the truck and trailer sliding from side to side," they said.
"The first one hit the rail and then the second wave came, and the trailer tipped overboard and it took the truck with it - it was quite impressive."
A fifth passenger described the weather as "really, really rough" heading into Wellington.
"I saw the chains on the truck snap and then as another wave hit us - it was sort out leaning towards the railing - and then the big wave that really hit us just flipped the whole truck over the edge.
"The railing on one side is completely gone and the next thing I know we're holding on for dear life - and the truck is floating beside us."
Monday afternoon's sailing was cancelled to allow for repairs to be carried out. Bluebridge hopes to have the ship back in service by Tuesday afternoon.
The Dutch-built Straitsman was built in 2005, and joined the Bluebridge fleet in 2010. It was formerly used as a ferry between the island of Bornholm and the Danish mainland.