Combustible cladding on the recessed balconies was the "main contributor" to the spread of fire in a Melbourne residential tower on Monday morning, the city's Metropolitan Fire Brigade said.

The fire, which started on a level 22 balcony just before 5am and spread to level 29 before it was extinguished, travelled quickly because of polyethylene-core aluminium panels running up the length of the 43-storey building, MFB deputy chief officer Adam Dalrymple said.