Mozambique opposition leader Venancio Mondlane returned home on Thursday, after fleeing in the days following a hotly contested October election that sparked demonstrations in which scores of protesters have been killed.

Mondlane says the October 9 poll was rigged and has called on his supporters to take to the streets across the southern African nation of 35-million.

A heavy riot police presence was felt in the areas surrounding capital Maputo's international airport where thousands gathered to welcome Mondlane.

A Reuters witness said tear gas was fired on crowds in the area and snipers were positioned on buildings around the air base.

Protests have continued, sporadically, for more than two months, and Mondlane's return could add fuel to the fire.

Civil society monitoring group Plataforma Decide said at least 278 people had died in the protests since mid-October, when the electoral commission announced the results extending the ruling Frelimo party's half-century in power.

Frelimo has ruled Mozambique since the end of the war against Portuguese colonial rule in 1975, clinging on throughout a 15-year civil war that killed a million people before a 1992 truce.

Last year's unrest hurt businesses and disrupted border access with neighbouring South Africa, while some people have fled to neighbouring Malawi and Eswatini amid the violence.

Mozambique's top court in December confirmed the ruling party Frelimo's election victory - despite multiple reports from observers that it was not free and fair - triggering a fresh round of protests.

Newly-elected President Daniel Chapo is to be sworn in next week, another potential flashpoint in Mozambique's political crisis.

Chapo and Frelimo deny accusations of electoral fraud.