A man has been found dead inside an apartment in Sydney's inner west after a "huge" fire erupted on Tuesday morning.

The fire caused a complete roof collapse of the Newtown unit complex at 310 Edgeware Road.

It was unknown whether residents would be able to return to their homes tonight.

The deceased man was not formally identified.

Thermal shock blankets and towels lay outside the apartment. ( ABC News: Paige Cockburn )

His small apartment was described by firefighters as a hoarder's home.

It was filled with books, furniture and a lot of other materials, which made firefighting efforts very difficult.

Authorities were yet to determine what started the blaze, which they were called to about 5.50am.

The residence was cordoned off as a crime scene and police were taking evidence from the building.

Police urged anyone with information in relation to the incident to contact Crime Stoppers.