Shots were heard near the presidential palace in the Madagascar capital of Antananarivo on Wednesday evening, hours after President Andry Rajoelina said an apparent attempt by a section of the military to seize power had failed, dpa reported.
The gunfire occurred on the day Madagascans voted on a new constitution for the Indian Ocean island.
Rajoelina ruled out stepping down, in a speech following an announcement by army General Noel Rakotonandrasana that the island's institutions had been suspended and a military committee had taken power.
"I am not afraid," Rajoelina said on national television.
Rakotonandrasana, ex-minister of the armed forces, made the announcement at a press conference at a barracks near Antananarivo's international airport. He was surrounded by about 20 officers as he spoke.
Colonel Charles Andrianasoavina, previously a supporter of Rajoelina, announced that the airport would be closed on Thursday and that the presidential palace would be stormed.
But Prime Minister Camille Vital spoke of a small number in the army who backed the officers and announced tough measures against all those who broke the law.
Eyewitnesses said some streets leading out of Antananarivo had been blockaded and tyres set alight.
At some polling stations voters were reportedly turned away because they were not on the register. But the voting was peaceful for the most part.
The referendum is part of a process to restore constitutional order to the Indian Ocean island, 20 months after Rajoelina, then opposition leader, ousted ex-president Marc Ravalomanana with help from the military.
Three opposition factions, representing Ravalomanana and two other former presidents, had called on the electorate to boycott the vote.
The new charter lowers the minimum age for presidential candidates from 40 to 35.
If passed it would mean Rajoelina, 36, whom the international community has shunned, could stand in presidential elections scheduled for May 2011, even though he has declared he will not be a candidate.
It also stipulates that presidential candidates must be resident in the country for at least six months prior to elections - a clause apparently aimed at barring the exiled Ravalomanana from staging a comeback.