Tanzania's former President Benjamin Mkapa, who ushered in multiparty democracy at home and worked to end conflict in East Africa, died in the early hours of Friday, President John Magufuli said.

Mkapa led several regional peace mediation initiatives as his country's third president between 1995 and 2005, and afterwards continued to seek reconciliation in Burundi, Kenya, Democratic Republic of Congo and the Great Lakes region.

He died while receiving treatment at a hospital in Dar es Salaam, Magufuli said in a statement, without elaborating.

"In Kenya we retain fond memories of his mediation efforts," said former Prime Minister Raila Odinga.

"(He) helped the country return to peace after the 2007-2008 election violence," Odinga said, referring to a period in Kenya when 1 200 people were killed in ethnic clashes resulting from a presidential vote whose outcome Odinga disputed.

"A statesman particularly remembered as an indefatigable peacemaker in the East African region," said the African Union Commission Chair Moussa Faki Mahamat.

Magufuli declared a seven day mourning period, during which all flags will be flown at half-mast.

"I am saddened by the death of our elder Benjamin Mkapa," Magufuli said in a tweet. "I will remember him for his love of country ... hard work and effort in building the economy. The nation has lost a strong figure."

Mkapa, 81, a former journalist, also served as an ambassador, foreign minister and leading official of the ruling CCM party.

Mkapa was first elected president in 1995 in Tanzania's first multi-party elections and oversaw macroeconomic reforms that helped stabilise a struggling economy and secured debt relief from foreign donors.

Born in southern Tanzania, Mkapa was an English graduate of the University of Makerere in Uganda and studied international affairs at Columbia University in New York.

"His efforts launched two decades of steady economic growth, fiscal credibility and falling inflation," said Aidan Eyakuze, executive director of civil-society body Twaweza East Africa.