Troops in the centre of Mali's capital have mutinied and the state's radio and TV broadcaster is off air with its headquarters surrounded by soldiers.
Heavy gunfire has been heard in Bamako and armoured vehicles sealed off the presidential palace.
It follows growing discontent among government troops as the Malian army struggles to contain advancing Tuareg rebels in the north of the country.
Earlier, soldiers were protesting about the lack of arms in their campaign.
AFP news agency reported troops stormed the Malian Radio-Television Office (ORTM).
The BBC's Alou Diawara in Bamako says there is a heavy presence of troops in the streets in the area around the building.
Earlier in the day, soldiers fired in the air as the country's defence minister started a tour of military barracks, just north of the capital.
The protest prompted an immediate strengthening of security around the presidential palace, with armoured vehicles sealing off the building.
Troops are also reportedly opposed to any potential talks with the rebels.
BBC West Africa correspondent Thomas Fessy says the soldiers want to express their anger at the way in which the government is handling the Tuareg-led rebellion.
He says Tuareg fighters have forced the army out of several northern towns over the past two months while Islamist combatants have also gained ground.
Earlier this week Ecowas, the West African regional organisation, urged its member states to support Mali with military equipment and logistics.
A presidential election is due to take place in the country in just under a month.
The government has so far refused to postpone the poll, despite the current unrest involving Tuareg-led rebels.