More than 100 people were evacuated from a Melbourne hotel after a man opened fire hydrants on 18 floors, sending water cascading through the building before he barricaded himself in an office.

When fire crews arrived at the Experience Bella Hotel Apartments in Southbank about 10:00pm, water was pouring out the front door and about 120 people inside were forced to leave by the stairs.

Police said a 27-year-old man had barricaded himself in an office after opening the hydrants and sending thousands of litres of water through the building.

The man, from Traralgon in eastern Victoria, was eventually arrested by police and taken to hospital by ambulance for assessment.

Guest Andrew Hannah from Ballarat was on an overnight getaway with his wife and 15-month-old daughter.

"A loud alarm went off — scared the hell out of me," he said.

"It couldn't have come at a worse time. It was a nice romantic night, so we were pretty unlucky in timing."

Mr Hannah said it was scary heading downstairs with a young child in ankle-deep water.

"Our instinct was to use the elevator but that wasn't the smartest thing to do," he said.

"It was pretty difficult to get down the stairs, really not knowing what was going on. It was quite scary."

The hotel was closed but guests were returning collect their belongings. ( ABC News: James Hancock )

Rebecca Hack, from Rockhampton, was in Melbourne for business.

She showed up at the hotel early this morning wearing her pyjama top after being forced to find another hotel for the night.

"I spent four hours outside in the cold, then found a hotel room and I've just climbed 24 flights of stairs to get my bag back," she said.

"I've got an 8.30am meeting. I didn't think a monkey pyjama top was the look."

Brisbane man Aidan Lockwood was in Melbourne celebrating his 23rd birthday at Crown Casino when he realised couldn't return to his hotel.

This morning, he went back to get his bags, shirtless, after running up and down 21 flights of stairs.

"[It] caused a whole lot of drama, a whole lot of grief for a whole lot of families," he said.

"There were mothers and kids out here at 11:30 at night."

Firefighters turned off the hydrants and used specialist fans and other equipment to dry out the hotel, which has extensive water damage.

Water was flowing out the front doors when fire crews arrived on scene. ( ABC News )

Authorities said the building would remain closed until it could be inspected.

One woman, Clare, said there was "water everywhere".

"I came into the city for a good night's sleep and I'll be lucky to get one," she said.

"On the 15th floor there was water everywhere, [we] couldn't use the elevator, had to walk down the stairs."

Fire crews were called back to the building around 4:30am when a maintenance worker was injured while trying to repair the fire panel.

The worker, 47, was hit in the face by a jet of water from a burst pipe. He was checked by paramedics and taken to hospital.

