Hundreds temporarily homeless after Melbourne's towering inferno

Hundreds of residents have been evacuated from a Melbourne apartment block as a wall of flames 21 storeys high consumed the building.

The LaTrobe Street building caught on fire at 2.30am today.

The building's 500 residents, most of them in pyjamas, were evacuated to street level as the fire raged.

Witness Rob Schofield said: "It was amazing how quickly it just shot up the building".

Eighty firefighters used cherry pickers and cranes to fight the blaze, as flames leapt from floor to floor.

"It just looked like a large fire on every floor, and spreading," said Ken Brown from the Metropolitan Fire Brigade.

Smoke alarms sounded and sprinklers were activated.

It took 45 minutes to control the fire, as hundreds of residents were led to Southern Cross station.

There they were given blankets, water and food.

Remarkably everyone, including families with small children, got out safely. 

"We treated most people just being cold, we did treat several people with skinned knees and arms cause they slipped on the wet steps coming down," said Stephen Moody from Ambulance Victoria.

By 8.30 this morning , Etihad Stadium had been transformed into an evacuation centre.

It was a refuge for every man, woman and child, as well as their furry friends.

Investigators say an air conditioning unit on the sixth floor sparked the blaze. It is thought products stored behind the unit restricted air flow and caused it to overheat.

Smoke and water damage on every floor is expected to lead to a bill of $5 million.