It is feared 21 have people have died in a plane crash in the sea off the Chile coast.
The air force plane had already failed to make two landing attempts on the remote Juan Fernandez islands before it disappeared from radar screens.
Search teams are heading to the area, but there are few hopes of any survivors.
“This is without a doubt a very hard blow for our country but I want to convey that, in these moments of anguish and uncertainty, is when we Chileans most need to unify and be in solidarity,” said President Sebastián Piñera.
The whole country is in mourning because among those feared dead is one of Chile’s most popular television personalities along with his four crew members from national television.
Felipe Camiroaga was planning a report on reconstruction on the islands, which were hit by a tsunami triggered by last year’s Chilean earthquake.
Island authorities say they have found debris and belongings in the water about a kilometre from the landing strip. Heavy winds and rain squalls had been preventing Camiroaga’s plane from landing.