Many school children are feared dead in an explosion on Sunday in Cameroon's restive Anglophone region of Northwest, according to witnesses and local police.

The blast occurred in the town of Nkambe, as children were taking part in activities to mark National Youth Day, which has been celebrated in the country on February 11 since 1966.

Witnesses told Xinhua the children had sustained "very serious" injuries.

Authorities are yet to make an official statement.

Separatists had imposed a three-day lock-down to disrupt the activities in the regions where they have been clashing with government forces since 2017 in a bid to create an independent nation they call "Ambazonia"