The bus is carrying a wide age range of passengers

The 15,000 mile trip Down Under has 39 intrepid passengers on board. The one-way trip has been organised by travel company Ozbus.

The company ruled out conventional long haul aeroplane flights in favour of the bus route, which takes in 20 countries, with one short flight at the end.

Among the inaugural passengers is a 66-year-old grandmother who is planning to return via container ship.

Ozbus Operations director, Australian Andrew Kelliher, said the company has been amazed by the popularity of the trip, which it believes to be the first ever regular overland coach service to Australia.

The journey will take in four ferries and has been made possible due to improved roads in Indonesia, explained Mr Kelliher.

"Some people have made it to Australia before using overland trucks, but previously the dirt tracks in Indonesia meant you could not take a bus," he told the BBC News website.

People are so used to flying the whole way to Australia and never seeing any of it

Andrew Kelliher, Ozbus

Together with company founder Mark Creasey, he has worked for the last 12 months sorting out the journey ready for Sunday's inaugural trip in the bus, a Belgian coach kitted out for longer travel.

The £3,750 one-way trip will stop every night for camping or hotel resting points and will take in Nepal, China, Malaysia and Indonesia among other places.

"People are so used to flying the whole way to Australia and never seeing any of it - this way you get to stop and look at it. It's pretty ground-breaking," said Mr Kelliher.

The journey also aims to please those concerned about carbon emissions - the only time passengers will take a flight is from East Timor across to Australia at the end.