Passengers onboard the Spirit of Tasmania II do not know when they will set sail after the ferry broke free of its moorings and crashed into a pier during wild weather in Melbourne.

Severe winds of up to 100 kilometres per hour swept across Melbourne and caused ferry to break free about 6:15pm Wednesday.

It swung at a 90-degree angle and crashed into the car bridge at Station Pier and drifted towards shore.

It also damaged its boarding ramp.

John Seaman is waiting to make the trip, from the Port of Melbourne to Devonport in Tasmania, and spent the night on board with other stranded passengers.

"They announced they'll be serving breakfast from about 7:00am," he said.

"So from that I gather that we won't be doing much before then.

"But during the night you could hear a few thumps and bangs.

"They were obviously working on the damaged part of the boat above us."

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Several tug boats were needed to turn the ship around.

The incident has also affected the scheduled sailing of TT-Line's sister ship Spirit of Tasmania I, which will remain in Devonport until engineers have assessed the damage in Melbourne.

In a statement, the operator said Spirit II passengers were safe and being kept updated.

After the ship was secured it was unable to take vehicles but passengers were allowed to board.

They were offered free food and refreshments drinks and were able to stay in their accommodation.

Vehicles cannot be unloaded and will remain onboard.

'A gust of wind came up' before mooring 'snapped'

Sorry, this video has expired Spirit of Tasmania ferry damaged in rough weather

Mr Seaman, who was due to take the 7:30pm journey across Bass Strait, said the noise of the impact took passengers by surprise.

"I was listening to the radio so I didn't hear it myself, but talking to people here they said that it just sounded like steel snapping, like rockets going off, and then the boat started to move around," he said.

"We were lined up to board the vessel and then a gust of wind came up and all of a sudden it appears the moorings snapped on the boat and it turned around on about a 90-degree angle.

"The damage to the gantry looks pretty severe, so what will happen from here no-one knows."

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Mr Seaman said the boat itself seemed to be in reasonable condition, with most of the damage confined to the pier.

He said that there were more cars onboard than there usually would be at such an early hour, because staff decided to begin boarding half an hour earlier due to Melbourne's extreme heat.

Another witness, Svedat Semerci, was swimming nearby with his son when he noticed the ship moving away from the pier.

"We started to realise the ship is moving away from the pier and it's really actually become apart from the pier," he said.

"I believe that everyone realised the ship was in trouble."

He saw the ship hit the bridge.

"The bridge that is attached to the ship ... ripped apart."

Mr Semerci said it was so close to shore it appeared to be sitting on the sand.

"It was trying to save itself and the water started to change colour. I don't know if it was oily or not, but the water turned to black and everyone got out of the water."

A photo taken from a commercial flight shows the ferry away from its moorings. ( Twitter: Matt Tinney )