Heavyweight investors, including Qatar's investment fund, have stumped up 5.45 billion US dollars for the Agricultural Bank of China IPO even before the share sale officially starts.

The offering, to begin Thursday, is on track to become the world's biggest, with pre-sale estimates soaring as high as 28 billion US dollars, outpacing the 22-billion-dollar offering by Industrial and Commercial Bank of China in 2006.

Dutch financial-services firm Rabobank will write a cheque for 250 million US dollars while Singapore state investment company Temasek Holdings is buying about 200 million worth of shares, Dow Jones Newswires reported, citing unnamed sources.

Australia's Seven Group Holdings, a media-to-heavy equipment firm controlled by billionaire Kerry Stokes, said Wednesday it is investing 250 million US dollars in the IPO which will see the last of China's big four banks float its shares.

The stock is slated to begin trading in Hong Kong and Shanghai next month.

The Qatar Investment Authority is set to be the single biggest investor with plans to buy 2.8 billion US dollars worth of shares, Dow Jones said.

The Kuwait Investment Authority will invest between 500 million and one billion US dollars in the share sale.

US food giant Archer Daniels Midland (ADM) will buy between 100 million and 200 million US dollars worth of AgBank shares.

ADM is one of the world's biggest food companies which produces goods from cottonseed and peanuts to ethanol and animal feed.

Tourism monopoly China Travel Services Group plans to invest 150 million US dollars while state-run consumer group China Resources (Holdings) is set to invest 200 million million US dollars, Dow Jones said.