A miracle survival took place in Madagascar on Tuesday when the country's secretary of state for police spent 12 hours in the open sea after a helicopter crash before reaching the coast unharmed.

A search was still ongoing for two other passengers after the crash that took place on Monday, the cause of which was not immediately clear, police and port authorities said.

Serge Gelle and a fellow policeman reached land in the seaside town of Mahambo separately on Tuesday morning, apparently after ejecting themselves from the aircraft, port authority chief Jean-Edmond Randrianantenaina said.

In a video shared on social media, 57-year-old Gelle appears lying exhausted on a deck chair, still in his camouflage uniform.

"My time to die hasn't come yet," says the general, adding he is cold but not injured.

The helicopter was flying him and the others to inspect the site of a shipwreck off the northeastern coast on Monday morning.

At least 39 people died in that disaster, police chief Zafisambatra Ravoavy said Tuesday, in an increase from a previous toll after rescue workers retrieved 18 more bodies.

Ravoavy earlier told Agence France-Presse (AFP) that Gelle had used one of the helicopter's seats as a flotation device.

"He has always had great stamina in sport, and he's kept up this rhythm as minister, just like a thirty-year-old," he said.

"He has nerves of steel."

Gelle became minister as part of a cabinet reshuffle in August after serving in the police for three decades.