The Industrial and Commercial Bank of China (ICBC) has issued a denial of rumors that its official website and trading system had been hacked on Wednesday.

The e-banking transaction speed of the ICBC's website became so slow that clients experienced severe difficulties in logging on to their on-line accounts.

Meanwhile, the speed of personal banking transactions at counters and ATMs were also crippled.

As clients lined up in front of the ICBC counters and ATMs waiting to draw money and sell funds, rumors spread that the bank had been attacked by hackers.

"Today is the first day of the lowered interest tax rate and the ICBC is upgrading its system," said an ICBC notice on its official website.

Wednesday was also the first day for most companies and institutions to pay pensions and salaries through the banking system. There were also fund issues, which put the system under further stress, said the notice.

All systems had returned to normal later in the afternoon and the ICBC apologized for the inconvenience, said the notice.

ICBC, China's largest commercial bank, had more than 2.41 million corporate banking clients and 170 million personal banking clients in 2006.

Other major Chinese commercial banks didn't report similar problems in their system.