A medical evacuation plane with seven people on board, including a French patient, disappeared west of Senegal during a flight from Burkina Faso to Dakar, the Senegalese civil aviation authority said in a statement.
The private Senegalair plane from Ouagadougou disappeared from radar screens at 708PM (1908 GMT) on Saturday 118 km (74 miles) west of the Senegalese capital.
Senegal's armed forces were conducting a search, the statement added.
The plane was carrying three crew members and medical staff, including a doctor and two nurses. Nationalities of those on board included two Algerians and a citizen of Congo, although the aviation authority did not specify whether it referred to the Democratic Republic of Congo or Republic of Congo.
The plane, chartered by SOS Medicin Senegal, left Ouagadougou at 430PM (1630 GMT), Burkina Faso's Minister of Transport, Daouda Traore, told Reuters. Ouagadougou is around 1,700 km (1,080 miles) southeast of Dakar.