Madagascar's defence ministry has told people living in and around an army barracks occupied by rebel soldiers that they should leave the area.
The officers, who said they had taken over the island nation two days ago, are holed up in the barracks near the airport of the capital Antananarivo.
Army chief Gen Andre Ndriarijoana later entered the barracks for talks with the mutineers.
Some were part of the coup that brought Andry Rajoelina to power in 2009.
The unrest came on the day of a referendum on a new constitution.
The vote is seen as a way of legitimising Mr Rajoelina's rule of Madagascar, which has been beset by instability for several years.
He has been diplomatically isolated since coming to power in March 2009 and has ignored attempts by regional mediators to broker a consensus with the opposition.
"We ask families living in the Ivato camp and residents of the surrounding area to temporarily leave the area for a safer place," AFP news agency quotes the defence ministry statement broadcast on national TV and radio as saying.
Correspondents say roadblocks have been set up in the surrounding area and schools have been evacuated.
Journalist Hannah McNeish told the BBC's Focus on Africa that shops are open in the capital and it seems like business as usual, although there is an air of apprehension and anticipation.
But she says there is a large security presence outside the base where negotiations are taking place.
After spending two hours at the barracks, Gen Ndriarijoana said the talks had gone well and would continue.
He said there were about 20 mutineers, adding that they may have political backing but for the moment it was being treated as a military matter.
On Wednesday, one of the coup bid leaders, Col Charles Andrianasoavina, said Malagasies were tired of waiting for a resolution to the political crisis that has seen the country lose much of its foreign aid.
If the new constitution is passed it would allow Mr Rajoelina to stay in power as long as it takes to organise an election.
It would also lower the age limit for presidential candidates from 40 to 35 years, meaning the 36-year-old to stand if he wanted.
Mr Rajoelina, who has said he will not run for president, organised huge rallies in support of a yes vote.
He is a former DJ and mayor of the capital city and rose to power on a wave of popular support.
But some analysts say his failure to end leadership squabbles has eroded some of his popularity.
In the run-up to the referendum there were many demonstrations against it - and all three of the main opposition groups, each led by an ex-president, called for a boycott.