By Glenn Cordingley from Perth Now

Perth is in danger of becoming one of the longest cities in the world - as the metropolitan sprawls north and south along an uninterrupted coast.

If you live in Perth's outer suburbs you've already heard the jokes about living in south Geraldton or north Bunbury.

But Perth's stretched suburbs clinging up and down the coast are already placing huge pressures on infrastructure and pose serious planning issues for the future.

There are real concerns that WA's predicted population explosion will stretch Perth into one of the world's longest cities.

Incoming WA premier Colin Barnett has identified this as a key factor facing the state and says he wants to redistribute the state's population away from the city.

Experts predict that by 2031, almost one million more people will join Mandurah in the south to Gin Gin in the north -- a distance of about 140km.

But demographer Bernard Salt believes the obsession with living by the sea could see an uninterrupted splurge of urban development spread as far south as Bunbury.

``The longest city is certainly a title that Perth really aspires to and I think it is very much on the cards in the not too distant future,'' he said.

``You could argue that southeast Queensland is longer, but technically there are urban breaks in between.''

He likened coastal Perth to Los Angeles, which stretches about 200km.