How long before someone is injured, This is the third bus powered by gas that has caught alight in the last couple of years......

Fresh concerns have been raised over driver and passenger safety on Perth buses after a fire tore through a gas-powered bus and forced the evacuation of the Esplanade Bus Port and some CBD offices.

The Public Transport Authority (PTA) said it was investigating the cause of the fire, which stopped services to the bus port for about two hours on Tuesday afternoon as fire crews extinguished the blaze and mopped up.

Thick smoke was sent over Perth's CBD and some offices near the bus port were evacuated.

Transport Workers' Union bus industry organiser Phil Ogden inspected the scene and said there was "nothing left" of the Transperth bus.

He said the driver and passengers on board at the time the fire broke out were very lucky to escape unharmed.

"It looks like a mess ... it's been burnt to the ground pretty much," he said.

Mr Ogden said he had spoken to bus driver who told him there was a water leak and he had turned off the engine at the time of the fire.

"The bus was stationary and the engine was off at the time because the driver had turned the engine off because of the water leak," he said.

The PTA said the bus was fitted with a fire suppression system, but Mr Odgen said the extent of the damage raised questions about the system.

 K.J.

Bright Idea;  When in Perth, take a taxi.