State-run Pakistan Television said Gen Musharraf, who is also army chief, had suspended the Constitution and declared emergency rule.

The move is expected to put off parliamentary elections due in January.

After news of the emergency rule spread, shots were heard in several neighbourhoods of Karachi.

There is strong backing for opposition leader Benazir Bhutto in Karachi and Sindh province. The most intense firing was heard in the Lyari neighbourhood, where support for her Pakistan People's Party is high, eye-witnesses said.

Ms Bhutto, who returned home from Dubai yesterday, was left sitting in a plane at Karachi airport.

She was waiting to see if she would be arrested or deported, her spokesman Wajid Hasan said after speaking to the former prime minister by telephone from London.

Witnesses said that around 100 paramilitary troops were deployed at Ms Bhutto's house.

Seven Supreme Court judges immediately rejected the move to suspend the current Constitution.

But Gen Musharraf responded by replacing Chief Justice Iftikhar Muhammad Chaudhry - a thorn in the government's side since the President's botched bid to sack him earlier this year - with Mr Hameed Dogar.

'Justice Hameed Dogar was administered the oath as Chief Justice by President Pervez Musharraf under the new provisional constitutional order,' a government spokesman said.

Gen Musharraf was reported to have justified the declaration on the grounds that 'some members of the judiciary are working at cross-purposes with the executive' and 'weakening the government's resolve' to fight terrorism.

The provisional constitution order allows courts to function but suspends some fundamental rights guaranteed by the Constitution, including freedom of speech. It also allows the authorities to detain people without informing them of the charges.

The government last night blocked transmissions of private news channels in several cities, and telephone services in Islamabad were cut.

As panic swept across the country, other telephone lines were jammed as people tried to find out what was happening.

Reaction was swift from Washington and London.

US Secretary of State Condoleezza Rice described Gen Musharraf's decision as 'very regrettable' while Foreign Secretary David Miliband said Britain was 'gravely concerned'.

Additional information from Reuters, AFP, AP

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