President Bingu wa Mutharika of Malawi has died, doctors and cabinet ministers have told the media, but the lack of a formal announcement is leading to widespread anxiety.
President Mutharika, who was 78 at the time of death, suffered a cardiac arrest the day before yesterday and he was flown to South Africa for treatment.
There are fears that his death could lead to a power struggle.
Both the U.K and U.S have called for the constitution to be respected.
According to the constitution, the vice-president takes over if the head of state is inca-pa-citated or dies in office.
However, Vice-President Joyce Banda and President Mutharika fell out after a row over the succession in 2010, and she was expelled from the ruling Democratic People's Party.
Mutharika's brother, Foreign Minister Peter Mutharika, was chosen instead of Ms Banda to be the DPP's presidential candidate in the 2014 elections.