One of the most architecturally dramatic features of the 2012 London Olympic buildings - the sweeping, wave-shaped roof to the aquatics centre - has begun to be lifted into place.

Designed by Iraqi-born architect Zaha Hadid, the centre will mark the gateway to the Olympic Park in Stratford, east London.

Originally estimated to cost 73 million pounds, it is now estimated to come in at 251 million pounds, despite the stingray-shaped roof being scaled down and redesigned amid cost fears.

A bridge connecting the roof to the main park will cost another 61 million pounds.

"The design of the roof is iconic and will be one of the lasting images of the London 2012 Games," said Sebastian Coe, chairman of the London 2012 Organising Committee, responsible for staging the Games.

The 160-metre long column-free roof is made up of steel, aluminium covering and timber cladding and will rest on two concrete supports at one end and a supporting wall at the other.

Erecting it will be one of the most complex engineering operations of the Olympic construction work.

The 17,500-seat centre will host swimming, diving and waterpolo during the Games, but will be reduced to 2,500 seats afterwards.