Simango, who headed the Democratic Movement of Mozambique (MDM) and was mayor of Beira port city, died in a private hospital in South Africa on Monday.
He had been airlifted to the neighbouring country on February 13 following a suspected coronavirus-related illness.
In a condolence message on Tuesday, Nyusi said Simango, aged 57, significantly contributed to the consolidation of democracy “through his dedication to the political and social life of the country, both as a party leader as well as a member of the State Council.”
“With his premature departure, Mozambique loses one of the most important voices in the country’s recent political history,” Nyusi said.
He said Simango’s contributions “created new values in the national political space” that consolidated efforts to promote peaceful and harmonious coexistence among Mozambicans.
Simango was elected mayor of Beira, widely considered Mozambique’s second city and an opposition stronghold, in 2003 and remained its leader until his death.
He was popular and known for running an effective municipal government, often seen leading from the front whenever the city has been hit by constant floods.