The bench ordered the arrest of Prime Minister Raja Pervez Ashraf in connection with accusations of graft over contracts awarded when he was power minister.

He has been ordered before the court on Wednesday.

The order was announced on television, immediately sending the Karachi stock exchange plunging.

This Supreme Court is regarded as hostile to the ruling Pakistan People's Party government, and has been activist in its pursuit of President Asif Ali Zardari, over separate corruption allegations, in particular.

The court dismissed Pakistan's previous Prime Minister Yusuf Raza Gilani last June, after he refused a court order to write a letter to Swiss authorities allowing them to investigate Zardari.

But the timing of the court's order has added to an already unstable atmosphere in the Pakistani capital.

This week in Islamabad, cleric Tahir ul-Qadri is holding his so-called "million-man march" to protest corruption and to demand the government hold elections immediately.

Elections are due in May.

Crowd numbers at Qadri's protest in Islamabad's central avenue are well below the million he promised, though there have been clashes with police.

Critics of Qadri say he is a stalking horse for Pakistan's powerful military and his movement might derail democracy all together, paving the way for the army, again, to take over the country.

Pakistan's 65 years as an independent country have been marked by regular military intervention in government.