China on Tuesday kicked off construction on one of the world's longest bridges linking southern Guangdong province to Hong Kong and Macau, a move seen to boost economic ties, state media reported.

The Y-shaped Hong Kong-Zhuhai-Macau Bridge, which Chinese officials presented as "the longest sea-crossing bridge in the world", spans nearly 50 kilometres (30 miles), the Xinhua news agency said.

When completed by about 2016, it will be longer than the 38.4-kilometre Lake Pontchartrain Causeway Bridge in the southern United States, which is often billed as the world's longest.

Hong Kong's Chief Executive Donald Tsang, who attended the groundbreaking ceremony with Chinese Vice Premier Li Keqiang, said the bridge would be "a crucial step forward for the social and economic integration" of the region.

"With a more efficient transport network, the finance, tourism, trade, logistics, and professional services in Hong Kong can be better (connected) to the west of the Pearl River Delta," he said, according to a statement posted on the Hong Kong government website.

The bridge will cut the driving time between Zhuhai and Hong Kong to 30 minutes from the current 3.5 hours and between Hong Kong and Macau to less than one hour from three hours, earlier Chinese media reports said.

The bridge, which will eventually be a six-lane expressway, will be built at an estimated cost of 73 billion yuan (10.7 billion dollars), Xinhua said.