Investigations are underway after one man was killed and another was seriously injured in a building collapse in Melbourne's south-eastern suburbs.

Frank Besanko from the MFB says part of the second storey floor collapsed at the construction site on Hawthorn Road Caulfield South around 10:00am (AEST), trapping two men.

"The roof part of the structure has actually collapsed on to the flooring of the first level and the flooring has subsequently collapsed again," he said.

"On the ground floor, there were two electricians working at the front of the shop that have escaped the fall however there were two males who weren't so lucky."

Police and fire crews worked to remove rubble from the injured men, but a 21-year-old man died at the scene.

A 48-year-old man was taken to the Alfred Hospital with suspected fractures in his arms and legs.

Two electricians were at the site escaped serious injury.

The injured man suffered broken bones and is being treated at the Alfred Hospital. ( ABC News )

One man who worked three doors away says the whole block shook when the floor collapsed.

An eyewitness, Nick, was walking home when he was asked by police to help out.

"A whole bunch of police had rocked up and they grabbed me and I just gave them a hand lifting a whole bunch of stuff out. Then I got out of there," he said.

The area has been cordoned off and emergency services remain at the scene.

It is the 11th workplace fatality in Victoria this year and WorkSafe is on the scene investigating.