ICBC's Shanghai-listed A shares surged 2.68% to 5.75 yuan, giving it a market capitalisation of $254bn, according to Reuters calculations.

That exceeded the $251bn capitalisation of Citigroup, previously the world's biggest bank, when its shares closed at $50.73 in New York on Friday. HSBC Holdings was in third place with $215bn.

Shares in ICBC, which listed in Shanghai and Hong Kong last October, have gained 15% this month on the back of a rally in China's booming stock market as well as strong growth in the bank's own earnings.

Weakness in Citigroup's share price, and appreciation of the yuan against the dollar have also shifted market values in favour of ICBC.

But some analysts believe ICBC's ballooning capitalisation may also be a sign of a dangerously overheated Shanghai stock market as speculating Chinese investors pour money into shares.

ICBC, a state-controlled behemoth which is trying to modernise a creaky branch network operating almost entirely inside China, reported income of $24bn last year.

Citigroup, one of the world's most sophisticated financial institutions with operations around the globe, reported income almost four times as large, at $90bn.

ICBC's share price yesterday valued it at 28 times analysts' forecasts for its earnings per share in 2007, far above 11 times for Citigroup and an average of 16 times for major global banks, according to Reuters Estimates.