Zambia's defence minister and presidential front-runner Edgar Lungu said on Tuesday the decision by interim president Guy Scott to dismiss him as the ruling party's secretary-general was illegal.

State radio in the southern African nation gave no reasons for Scott's surprise removal of Lungu from his top post in Sata's Patriotic Front (PF) party, which came to power after elections in 2011.

Scott became Africa's first white leader in 20 years after the death last week of President Michael Satan Sata. Scott is constitutionally barred from running for president because his parents were born in Scotland.

"The is illegal and highly provocative under the current environment in which we are mourning our late president," Lungu said in a statement read out on state ZNBC Radio on Tuesday.

Scott late on Monday named his replacement as Davies Mwila, although he turned down the appointment.

"In our tradition it is taboo for us to do anything like that before you bury," Mwila said separately on ZNBC Radio.

Lungu said he has called for an emergency meeting of the PF central committee on Tuesday to discuss his dismissal.

Police in Lusaka on Monday night fired tear gas to stop protests by students and PF members who took to the streets over Lungu's dismissal.

Lungu, who is also justice minister, had often stepped into Sata's shoes as 'acting president' in the last year. Many Zambians had considered him the person most likely to win the presidential elections that are due by the end of January.

Other possible contenders include former justice minister Wynter Kabimba, finance minister Alexander Chikwanda and Sata's son Mulenga, who is currently mayor of Lusaka, a position his father occupied in the 1980s.

The decision by Scott, a Cambridge-educated economist, to dismiss Lungu from the helm of the PF is also likely to fuel speculation he may seek to run for the presidency, regardless of the constitutional restrictions.