Two people have been taken to hospital after a leak of vile smelling gas in a Collins Street office block led to the building's evacuation.
The incident began about 8am on Tuesday on the 27th floor of 35 Collins Street in Melbourne, with about 24 firefighters called, an MFB spokesman said.
"Initially a couple of people were affected by the gas and alerted the brigade," he said.
"Some batteries, from their internal systems became compromised and were giving off hydrogen sulphide gas."
Multiple floors of the building, level 17 to 32, were evacuated, as firefighters attempted to isolate the battery source and disperse the gas - which is noted for it's rotten egg smell.
???Paramedics assessed five people at the scene, of which two were taken to hospital, an Ambulance Victoria spokeswoman said.
A woman who was unwell and a man with chest pains were both taken to St Vincent's Hospital, in stable conditions.
The MFB spokesman said it took fire crews two hours to declare the incident under control.
"Our hazmat and breathing apparatus appliances are on scene to enable atmospheric monitoring of the environment and safe storage of the compromised batteries," he said.
The floors were evacuated for about three hours, with people let back in after 11.30am.