Musharraf, who seized power in a 1999 coup but had given a conditional pledge to step down as military chief and become a civilian president this year, declared a state of emergency Saturday night, dashing recent hopes of a smooth transition to democracy for the nuclear-armed nation.
"Gen. Musharraf's second coup," said the headline in the Dawn daily. "It is martial law," said the Daily Times.
"A lot of people here are left in a state of disbelief," reports CBS News' Farhan Bokhari from Islamabad.
Authorities began rounding up opposition politicians despite calls from Washington and other Western allies not to take authoritarian measures.
Across Pakistan, police arrested political activists and lawyers at the forefront of a campaign against military rule. Among those detained were Javed Hashmi, the acting president of the party of former Prime Minister Nawaz Sharif, and Asma Jehangir, chairman of the independent Human Rights Commission of Pakistan.
U.S.-allied Musharraf removed the country's chief justice just as the Supreme Court was to rule on whether to validate his recent election as president by a largely Musharraf-friendly Parliament.
Hashmi said Musharraf usurped the independence of the judiciary "to save his own illegitimate rule."
"But he cannot survive against the people's outrage," Hashmi told reporters as he was led away with 10 aides in the central city of Multan.
Private Geo TV said in a report via satellite that authorities arrested Aitzaz Ahsan, a lawyer who represented the chief justice when Musharraf unsuccessfully tried to fire him earlier this year.
Another opposition party leader, Imran Khan, was put under house
"The only reason why he's passed the emergency is because he was scared that the Supreme Court would not allow a military general to fight the election of the president," Khan told CBS News correspondent Mark Phillips. "And what is going to happen in Pakistan is that it's going to head towards anarchy, there will be more militancy in the country."
Scores of paramilitary troops blocked access to the Supreme Court and parliament. Otherwise the streets of the capital appeared calm.
Local newspapers and opposition leaders - including key Musharraf rival Benazir Bhutto, the former prime minister who returned last month from eight years in exile - accused the general of imposing martial law without announcing it.
But his government denied this. Attorney General Malik Mohammed Qayyum noted that the prime minister and parliament were still in place.
"There is no martial law in the country. Only a state of emergency has been declared," Qayyum said. "The civilian government will continue to function."
The U.S. called for Musharraf to restore democracy. However, the Pentagon said the emergency declaration does not affect U.S. military support for Pakistan and its efforts in the war on terrorism. Britain said it was deeply concerned.
Musharraf's leadership is threatened by an increasingly defiant court, the reemergence of political rival and former prime minister Benazir Bhutto and an Islamic movement that has spread to Islamabad. He said Pakistan was at a "dangerous" juncture and extremists had directly challenged the government's authority.
"The extremism has even spread to Islamabad, and the extremists are taking the writ of the government in their own hands, and even worse they are imposing their obsolete ideas on moderates," the president said in an address to the nation late Saturday on state-run television.
"Inaction at this moment is suicide to Pakistan and I cannot allow this country to commit suicide," he said.
Musharraf replaced the chief justice of the Supreme Court - who had emerged as the main check on his power - before a crucial Supreme Court ruling on his future as president. His emergency order accused some judges of "working at cross purposes with the executive" and "weakening the government's resolve" to fight terrorism.
He criticized the Supreme Court for failing to make a ruling yet on whether to validate his contentious victory in a presidential election, and for punishing government officers, including police. He said this had left the government system "semi-paralyzed."
Seven of the 17 Supreme Court judges immediately rejected the emergency, which suspended the current constitution. Police blocked entry to the Supreme Court building and later took the deposed chief justice and other judges away in a convoy, witnesses said.
In his television address, Musharraf said he hoped democracy would be restored following parliamentary elections.
"But, in my eyes, I say with sorrow that some elements are creating hurdles in the way of democracy," said Musharraf, who was wearing civilian clothes and spoke firmly and calmly. "I think this chaos is being created for personal interests and to harm Pakistan."
Speaking in English, Musharraf said he wanted to explain his actions to the United States and the West, reports Phillips.
"Please also do not demand your level of human rights, civil rights, civil liberties which you learned over the centuries. We are trying to learn and we are doing very well also, please give us time," he said.
Musharraf even quoted from Abraham Lincoln, citing a letter Lincoln had written suspending some constitutional provisions during the Civil War, adds Phillips. What Musharraf did not do, however, is say whether the elections planned for next year will actually happen.
The emergency comes as Musharraf's security forces struggle to contain pro-Taliban and al-Qaida-linked militants who have gained control of large tracts of the volatile northwest, near Afghanistan.
Violence has reached major cities with deadly suicide attacks in Islamabad and Karachi underscoring the failure of Musharraf's administration to combat the threat, despite huge financial support from the United States.
Talat Masood, a retired Pakistani general and respected analyst, said the emergency declaration was a pre-emptive move in case the court ruled against him, and said the move could "further aggravate terrorism and extremism in the country and slide the country into anarchism."
Rick Barton, a Pakistan expert at the Washington-based Center for International and Strategic Studies, said Musharraf's move Saturday was like throwing a "wet blanket" on the problem.
"He's obviously not very popular, and it's not going to increase his popularity," Barton said. "Unless he develops a new line or is able to be more effective with his old line, he seems to be just buying time, an inevitable delay to his demise."
The order drew swift complaints from the United States and Britain - Musharraf's main Western allies. Secretary of State Condoleezza Rice urged restraint on all sides and a return to democracy.
The United States "does not support extraconstitutional measures," Rice said from Turkey, where she was participating in a conference with Iraq's neighbors.
Musharraf claimed that 61 terrorists have been freed on order from the court - an apparent reference a case that has been led by the now-deposed chief justice to press authorities over suspects held by intelligence agencies without charge.