A fire broke out early Wednesday at the Pakistani hospital where former military ruler Pervez Musharraf was admitted for a heart condition, officials said.

"There was a small fire incident at the hospital, but it was extinguished immediately," a source at Armed Forces Institute of Cardiology in Rawalpindi told AFP.

Another source confirmed the fire incident was "of a minor nature".

Officials said the cause was being investigated and may have been started by an electrical short circuit.

Musharraf was taken to hospital last week after falling ill while travelling to a special court considering treason charges against him.

He was diagnosed with coronary artery disease, with his lawyers pleading for him to be allowed to receive treatment abroad.

Musharraf's lawyer Ahmad Raza Kasuri said that the former president was not affected.

"He is safe as the fire incident happened on another floor," Kasuri told AFP.

The court has ordered Musharraf to appear in person on Thursday, after considering a medical report on his heart complaint. The case has gripped the nuclear-armed nation for the past fortnight.

Musharraf has yet to appear in person before the specially-convened three-judge tribunal, missing hearings due to security fears and the health scare.

Rumours have circulated for months that a backroom deal would be struck to whisk him overseas to avoid a destabilising clash between the government, which brought the charges, and the powerful armed forces.

Musharraf's camp says the treason allegations, which relate to his imposition of emergency rule in November 2007, are politically motivated, and his lawyers have challenged the authority of the tribunal.

But the former commando has said he wants to stay and fight the charges.

Aside from the treason allegations, Musharraf also faces trial over the assassination of former prime minister Benazir Bhutto, the death of a rebel leader, a deadly raid on a radical mosque and the detention of judges.