Medical sources say Malawian President Bingu wa Mutharika has died after suffering a heart attack, but there has been no official announcement of his death.
Diplomatic sources say the president, 78, collapsed after falling ill at his home in the capital, Lilongwe, on Thursday.
He was rushed to a local hospital, where sources say he died. However, the Malawian government has yet to issue a statement on the president's condition.
Malawi's former president, Bakili Muluzi, urged officials on Friday to release information about Mutharika.
"The present where the government is almost silent on the health status of the president is very unfortunate, and ought not to continue," said Muluzi. "It is the constitutional duty and indeed good practice of the government to inform its citizens and the world community timely, accurate and transparent information about the particulars of the ongoing treatment and health condition of their sick president."
He also called on politicians to respect the constitution, which states the vice president, Joyce Banda, should take power if the president is incapacitated.
"My humble appeal to all politicians involved both in government and those in opposition is that they should put the interest of the country ahead, as we anxiously await to hear from the doctors attending upon our president." added Muluzi.
Mutharika was elected president of Malawi in 2004 and won a second term in 2009.
He was credited with improving food security in Malawi and, at one time, making his country a political and economic model for other African countries.
But in more recent years, the economy has stumbled and unemployment has been high. Critics of the president say he had become increasingly autocratic. Nineteen people were killed last July in anti-government protests.
An economist by education, Mutharika was a World Bank official and served as a civil servant in Malawi. He was appointed minister of economic planning and development in 2002 and then-President Muluzi nominated him as his successor.
Mutharika heads the ruling Democratic Progressive Party, which has the majority in parliament.
Some information for this report was provided by Reuters.