Philippine President Rodrigo Duterte is expected to declare a ceasefire on Saturday to reciprocate a week-long truce that the communist rebels have announced.

Presidential communication secretary Martin Andanar said that Duterte has "expressed his willingness to reciprocate" the ceasefire that the rebels announced on Friday night, Xinhua news agency reported.

"As to the official announcement, we should be expecting it within the day," said Andanar, adding that details of the government ceasefire will be announced later.

"As to the date, the schedule and how long the ceasefire will be (are) still under discussion between Duterte and Presidential Peace Adviser Jesus Dureza and Defense Secretary Delfin Lorenzana," he said.

The Communist Party of the Philippines on Friday declared a seven-day unilateral ceasefire ahead of the resumption of peace talks in Oslo, Norway, that starts on Monday.

The rebels said the ceasefire will take effect from 12.01 a.m. on August 21 and will last until 11.59 p.m. on August 27.

"This ceasefire declaration is encouraged by the (Philippine government’s) facilitation of the release of the nearly all National Democratic Front of the Philippines consultants who are set to participate in peace negotiations in the course of the next several months," the rebels said in a statement.

The formal talks will start on August 22 and will continue until August 26.