The C-130 Hercules cargo plane vanished after departing an air base in the southern city of Punta Arenas Monday at 4:55 pm (19:55 GMT) en route to Chile's Antarctic base of Eduardo Frei, officials said.

Contact was lost with the plane at 6:13 pm (2130 GMT), the Chilean Air Force said, adding that the plane had enough fuel to remain in the air for several hours beyond that time.

But seven hours after losing communication officials declared that the plane had crashed.

The pilot may have carried out an emergency ocean landing, said Eduardo Mosqueira, commander of the Fourth Brigade based in Punta Arenas, early Tuesday.

"All national and international air and maritime means available in the area are continuing the search" for survivors, the air force said in a statement Tuesday.

Aircraft and ships from Uruguay, Argentina and Chile have joined in the search, officials said.

Chilean President Sebastian Pinera cancelled his scheduled trip to Buenos Aires on Tuesday for the inauguration of Argentina's new president Alberto Fernandez to monitor rescue operations from Santiago, government spokeswoman Karla Rubilar said.

He initially said that he would travel to Punta Arenas.

"We are doing everything humanly possible to find them despite extremely difficult conditions," Pinera said.

- Good weather conditions -

The plane went missing while flying over the Drake Passage, a maritime route between South America and Antarctica frequently hit by some of the world's worst weather.

However, the weather conditions "to fly were good, which is why the trip was planned," said Francisco Torres, head of operations of Chile's air force.

The planes and ships are searching within a 60-mile radius from where officials lost contact with the Hercules, Torres said.

Defense Minister Alberto Espina flew to Punta Arenas with Air Force chief Arturo Merino to coordinate the search and rescue mission.

"Believe me, we are using all human and material means at our disposal, with planes, ships, satellites, and foreign support to try to find them," Espina told journalists. "We know that the conditions are very difficult."

Brazil has sent a Polar exploration ship and two air force planes to join the search.

The names of those aboard the missing airplane were released Tuesday. Most were air force personnel, but also included three people from the army, two from a private construction company and an official from a Chilean university.

Many of them were traveling to carry out logistical support tasks at the Eduardo Frei base.

Air force officials said they were in contact with the families of those on the plane.

The plane did have an emergency positioning system, but it did not appear to be working during the early morning search, said Mosqueira.

The disappearance of the C-130 came as Chile struggles with nearly two months of protests over social and economic inequality, and against an entrenched political elite.

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

In September 2011, a Chilean military plane with 21 people aboard crashed near Robinson Crusoe Island, in the Pacific some 700 kilometers west of the South American mainland. A popular TV show host was among the victims.