A man who briefly attacked a fire truck on its way to a job in Melbourne has climbed back on the vehicle's roof on its return from the emergency, before falling and knocking himself out.

Fire crews had their vehicle set upon near Victoria Street in Richmond about 8:00pm while they were on their way to a fire in A'Beckett Street in the city.

The Metropolitan Fire Brigade (MFB) said the truck was blocked by a man who stood in front of the vehicle and then forcibly tore off a wiper blade.

He then banged on the windscreen repeatedly, the MFB said.

Loading

MFB deputy fire chief David Youssef said such attacks were "extremely reckless, at best".

"They were a little bit shaken by what occurred but they're extremely professional and they actually dealt with it very well," he said of the fire crew caught up in the incident.

The fire truck moved around the man and continued to the scene.

When the fire truck returned, the crew saw the same man lying on the bonnet of a car in Victoria Street.

They stopped to check on him and he started attacking the truck again and climbed on the roof.

Fire crews were stuck inside the vehicle while they waited for police to arrive.

The man slipped from the fire truck and fell head first onto the concrete and knocked himself out.

He was taken to hospital with serious injuries.

MFB chief officer Peter Rau said on Twitter the attack was "unacceptable".

The incident follows an attack on two paramedics and their ambulance earlier this month.

Three people have been charged over that incident.