The government department investigating Victoria's flammable cladding crisis is housed in a tower deemed such a high fire risk that it requires constant surveillance and a direct phone line to the nearest fire station.

Internal emails seen by The Age detail that the Department of Environment, Land, Water and Planning building in Nicholson Street is clad in non-compliant aluminium panels, a discovery believed to have been made under an audit of all state government buildings.

The audit is being done by the department and the Victorian Cladding Taskforce.

The emails also reveal that only weeks before the "robust" safety measures were implemented, a fire had to be extinguished in a lane next to the 18-storey building on the corner of Victoria Parade.