Seventeen of those on board the C-130 aircraft were crew and the others were passengers, Chile's Air Force said Monday.

The plane is considered to have crashed and "all national and international air and maritime means available in the area are continuing the search (for survivors) in the sector where communications were lost with the aircraft," it added in a statement Tuesday.

The four-engine aircraft took off Monday at 4.55 pm (19:55 GMT) from an air base in Punta Arenas in Chile's far south and contact was lost at 6:13 pm -- a little over an hour after it took off.

Those on board were to carry out logistical support tasks at Chile's Eduardo Frei Antarctic base -- the country's largest, the Air Force said.

Personnel were also being transferred to inspect the base's floating fuel supply pipeline and undertake anticorrosive treatment of the facility.

The plane did have a satellite positioning system, but it did not appear to be working during the early morning search, said Eduardo Mosqueira, Commander of the Fourth Air Brigade.

President Sebastian Pinera, whose country has been witnessing its worst civil unrest in decades, said in a tweet he would fly to the southern city of Punta Arenas with Interior Minister Gonzalo Blumel.

Once there, they would meet up with Defense Minister Alberto Espina to monitor the search and rescue mission, which was underway using aircraft and navy vessels.

The plane's disappearance is the latest incident in a country where Chileans have for nearly two months protested social and economic inequality, as well as an entrenched political elite.

The crisis and its violent demonstrations have led to 26 deaths and more than 12,000 injuries, according to the Organization of American States.