The head of Guinea's armed forces along with 10 other people including five top Guinean military officials have been killed in a plane crash in Liberia.

The Casa CN-235 plane, carrying a military delegation from Guinea to mark Liberia's annual Armed Forces Day, crashed near the Liberian capital, Monrovia on Monday.

"The accident claimed the lives of the six members of the delegation led by General Souleymane Kelefa Diallo, chief of staff of the army, and the five members of the crew," Guinea's Defense Minister Abdoul Kabele Camara said in a statement.

Liberian President Ellen Johnson-Sirleaf visited the site of the crash and declared a national day of mourning for Tuesday.

"May all of us pray for the souls of the Guineans who died in the crash," she said.

The investigators have not yet determined the cause of the crash.

Emergency workers had found the plane's flight recorder (black box) and will send it to Canada for analysis.

Guinean President Alpha Conde named Camara's deputy General Namory Traore as interim chief of staff.

The CASA CN-235 is a medium-range twin-engined transport plane that was jointly developed by CASA of Spain and Indonesian manufacturer IPTN, as a regional airliner and military transport.