State television carried the state of emergency announcement Saturday evening, hours after independent news channels in the country reported a declaration was imminent.
A broadcaster for the state television read a statement attributed to the chief of army staff, which is the other office President Musharraf holds.
He said the chief of the army staff has imposed a state of emergency and issued a provisional constitution.
There was no further explanation for the announcement.
Phone lines have been cut and independent news channels have gone off the air. Army vehicles took up positions on key roads in Islamabad and surrounded the Supreme Court, where several top judges are believed to be located.
The move follows a series of suicide attacks on official and military targets in recent weeks, as well as an ongoing battle with militants in northwestern Pakistan's Swat Valley.
Former Prime Minister Benazir Bhutto left Pakistan on Thursday to visit family in Dubai.
Several key cases regarding the country's political leadership are under consideration in the Supreme Court, including a constitutional challenge to President Musharraf's unofficial re-election.
Pakistan's legal community has been a fierce critic of Mr. Musharraf after he tried to remove the nation's chief justice from his office in March.
Following the state of emergency announcement, judges on the court told independent news channels they would try to strike down the measure.