Police and demonstrators battled in Malawi's capital Lilongwe on Tuesday before troops intervened to restore calm, in the latest protests against the outcome of presidential elections, witnesses said.
Demonstrations have been regularly staged since the May 21 elections, aimed at forcing out Electoral Commission chairwoman Jane Ansah over her handling of the poll.
The protest organisers, the Human Rights Defenders Coalition, had dubbed Tuesday's rally the "One Million March," in a quest to draw a million marchers to the cities of Lilongwe, Blantyre and Mzuzu.
A Lilongwe-based journalist, Golden Matonga, estimated the turnout in the capital in the hundreds of thousands.
In commercial centre of Blantyre, more than 20,000 took part.
Participation was slightly lower in Mzuzu, the landlocked southern African country's third largest city, sources said.
While the protests in Blantyre and Mzuzu were generally peaceful, the Lilongwe event was marred by violence, including the burning of a police armoured vehicle.
Calm return after the military was deployed, witnesses said.
Residents said they had seen cars being torched and shops looted.
"Apart from the police vehicle, I saw at least two other government vehicles being burnt and shops literally being ransacked along the path of demonstrations," local resident Patrick Banda told AFP.
The unrest began after police had fired teargas to try to disperse the crowd, and people retaliated by setting fire to the police vehicle.
Months of protests have erupted in usually stable Malawi since President Peter Mutharika won a second term against MCP leader Lazarus Chakwera.
The opposition alleges fraud, saying that many vote tally sheets were altered using typewriter correction fluid.
It has filed a lawsuit to try to overturn the outcome.
On Monday, the High Court threw out a petition by the country's attorney-general, who had sought to ban protests.