Pakistan's opposition on Thursday called on Prime Minister Imran Khan to resign ahead of a parliamentary vote which could see the ouster of former cricket star and the return of political uncertainty in the nuclear-armed country.

Khan, 69, has been facing mounting criticism of his performance, including his management of an economy beset by high inflation and rising deficits, and he lost his majority in parliament on Wednesday when a main ally quit his coalition.

"We want to send Imran Khan a message that there is no safe passage for you," opposition leader Bilawal Bhutto Zardari, son of assassinated former Prime Minister Benazir Bhutto, told reporters at parliament. "I want to give you a suggestion that you take an honorable exit, and an honorable exit is that you resign today and let the opposition leader take oath of the leader of the house."

Khan is due to address the nation on Thursday, while parliament votes on whether to remove him as prime minister on Sunday at 11.30 a.m. (6:30 a.m. GMT).

"The prime minister is as good as gone," the influential Dawn newspaper said in an editorial on the front page of its website on Thursday.

On Wednesday, Khan's main parliamentary ally, the Muttahida Qaumi Movement (MQM), abandoned his coalition and threw its lot in with the opposition seeking to oust him.

Opposition leaders had called on Khan to resign even before he lost his majority in parliament, but his aides have said he will not quit.

Khan's ouster could mean another round of instability in a country in which the military has a long record of intervening in politics and no prime minister has ever completed a full five-year term.

Political analysts argue that Khan enjoyed the support of the military when he won an election to become prime minister in 2018 but he later lost the generals' favor over various wrangles.

Khan has denied ever having the backing of the military and the military, which has ruled Pakistan for about half its history, denies its involvement in civilian politics.