Pakistan's former military ruler Pervez Musharraf was rushed to hospital Thursday after suffering a "heart problem" on his way to court in the latest dramatic twist in his treason trial.

The 70-year-old had been summoned to the special tribunal in Islamabad after failing to show up for two previous sessions due to security threats against him.

Jan Mohammad, a senior police official, told the court that Musharraf had fallen ill with a "heart problem" while being transported to the hearing under heavy guard.

He was undergoing tests at the Armed Forces Institute of Cardiology in Rawalpindi, the garrison city bordering Islamabad.

An aide to the ex-general, who is facing a series of criminal cases dating back to his 1999-2008 rule, told AFP he was in "bad shape".

His spokesman Raza Bokhari said in an emailed statement Musharraf was conscious and "oriented in time and space" and was being examined by military doctors.

His wife has arrived at the hospital and his daughter is on her way from Karachi, a source said. A doctor who spoke on condition of anonymity said he was in a stable condition.

The treason hearing was adjourned till Monday, with Musharraf's legal team saying he would seek medical advice before deciding whether to attend.

The team 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 three-judge tribunal.

A source from the former ruler's camp said efforts were under way to fly Musharraf out of Pakistan.

There have been longstanding rumours of a deal to whisk him out of the country to avoid a destabilising clash between the government, which brought the charges, and the powerful armed forces.

But Musharraf has previously insisted he wants to fight the charges against him.

Musharraf is Pakistan's first ex-army head to be put on trial. While there has been no public comment on the case from the military, some observers say they are reluctant to have their former chief suffer the indignity of trial in a civilian court.

The government of Prime Minister Nawaz Sharif has repeatedly said it would not let Musharraf, currently under a travel ban, leave Pakistan before facing trial.

Sharif was the man Musharraf ousted from power in his 1999 coup, and his lawyers have previously said the case is an attempt to settle old scores through the courts.

Some commentators have complained it is an unnecessary distraction at a time when the country is struggling with a bloody homegrown Taliban insurgency, crippling gas and electricity shortages and a faltering economy.

Security was tight at the hospital in Rawalpindi, an AFP journalist said, with soldiers and paramilitary Rangers standing guard.

Lawyer walkout

Earlier on Thursday his lawyers walked out of court, complaining of being threatened and harassed.

Anwar Mansoor Khan, one of the lawyers, told the court he has been receiving threats and was unable to sleep the night before the hearing.

"I was under total threat... from 1:00 am to five in the morning. Someone was banging on my door and ringing my bell," Khan told the court.

When one of the judges asked who was threatening him, Khan answered: "This very government."

The court promised to investigate but Khan walked out of the courtroom, followed by other members of Musharraf's legal team.

Sharifuddin Pirzada, another of Musharraf's lawyers, also complained that he had been threatened.

Khan told the court on Wednesday he had been attacked in his car while travelling to the eastern city of Lahore following an earlier hearing.

The treason allegations are the latest in a series of criminal cases faced by Musharraf since he returned to Pakistan in a thwarted bid to run in last May's general election.

These include murder charges over the assassination in late 2007 of former prime minister Benazir Bhutto.

On Sunday, the retired general denounced the treason case as a "vendetta" against him and claimed he had the backing of the military.

The potential for the case to disrupt Pakistan's delicate civilian-military balance means it will be keenly watched by the US and NATO as they wind down their mission in neighbouring Afghanistan.