Four people, including two teenagers, are stranded in Bass Strait after the engines of boat failed.

Water police launched a rescue operation this morning after receiving a mayday call from the boat just before 9am.

Four people are on board the 12.5-metre steel vessel that hit trouble about 50 kilometres off Victoria's coast.

A Victoria Police spokeswoman said the boat was heading towards Deal Island in Bass Strait, where the vessel was due to be dropped off, when the crew sent out a mayday call saying their engine had failed.

Shortly afterwards the boat's communications system also failed, she said.

The police air wing was sent out to search for the boat and located it about 50 kilometres from land.

The air wing dropped a rescue package, including a satellite navigation system, to the crew, which consists of two men and two teenagers, aged 15 and 16.

The police air wing will continue to monitor the boat until water police from Williamstown can reach the stranded vessel, expected to be about 12.30pm.

The boat will then be towed back to Port Welshpool, where it is expected to arrive about 5pm.

The spokeswoman said sea conditions were favourable, with swells of between half and one metre and winds of about 28km/h.