Two Malagasy journalists, Ms Lalatiana Rakotondrazafy and Mr Fidèle Razarapiera, are being detained at an Antananarivo police station over work-related accusations.
The Free FM radio employees were seized Wednesday night.
Police officers spent about seven hours interrogating the journalists before detaining them.
The journalists' lawyer, Mr Andry Fiankinana, said their continued confinement was in contravention of the law.
Media representatives have expressed concern over Madagascar's hostile environment for journalism operations.
They expressed their concerns during the World Press Freedom Day celebrations Wednesday in the south-western regional capital of Toliara.
We are concerned about the situation. The state has made it difficult for the Malagasy journalists to enjoy the World Press Freedom Day with the rest of their colleagues the world over, said
Mr Rocco Rasoanaivo, the President of the Madagascar journalists’ union (SJM).
SJM planned to hold a street demonstration in the capital Antananarivo to demand more freedom for the press in Madagascar.
Ms Rakotondrazafy is the acting general-secretary for SJM.
Meanwhile, Free FM radio station has continued to play songs calling for patriotism despite the threats to its operations.
The station's listeners have since Wednesday night organised themselves to protect the media house, now threatened with closure.
“We condemn the absence of the press freedom in Madagascar as we celebrate the World Press Freedom Day. We ask the authorities to accept true democracy,” said Ms Hortense Rasoarimanana, the secretary-general of the Free FM listeners’ club.
Several people have called for general uprising across the country and the immediate release of all detainees.
“We ask all of the listeners to stand up to battle the injustice as the fight is not yet over,” said Mr Tsiry Rasoarivelo, the head of the Free FM Young Association.
The head of Madagascar Green Party and one of the potential candidates in the next presidential poll, Ms Sarah Georget Rabearisoa, also condemned the detention of the two journalists
Ms Rakotondrazafy and Razarapiera were last week summoned to appear before the criminal investigation officers.
They were accused of defamation, propagation of false news and insult following their comments regarding a young native billionaire who is a close ally of President Andry Rajoelina.