Pakistan's anti-graft watchdog arrested former Prime Minister Imran Khan at Islamabad High Court on Tuesday, in a dramatic move that threatens fresh turmoil in the nuclear-armed country.

Footage of the arrest showed scores of security personnel in riot-control gear whisking Khan away in a van as Khan's party called for protests across the country.

"Pakistan's people, this is the time to save your country. You won't get any other opportunity," the Pakistan Tehreek-e-Insaf (PTI) party wrote on Twitter.

The arrest comes at a time when ordinary Pakistanis are reeling from the worst economic crisis in decades, with record high inflation and anaemic growth.

An International Monetary Fund bailout package has been delayed for months even though foreign exchange reserves are barely enough to cover a month's imports.

Interior Minister Rana Sanaullah told reporters that Khan was arrested by the National Accountability Bureau (NAB) after he did not appear before it "despite notices".

The NAB had issued Khan's arrest warrants on May 1, according to an order seen by Reuters. "Khan is accused of commission of the offence of corruption and corrupt practices," it said.

Khan's graft case is one of over 100 registered against him since he was ousted from power in a parliamentary vote in April last year. He served four of his five-year term.

In most of the cases, Khan faces being barred from holding public office if convicted, with a national election scheduled for November.

Previous attempts to arrest Khan from his Lahore home resulted in heavy clashes between his supporters and law enforcement personnel.

Political infighting is common in Pakistan, where no prime minister has yet fulfilled a full term and where the military has ruled for nearly half of the country's history.r