Two people died when a Dutch army helicopter crashed into the sea soon after take-off from the Caribbean island of Aruba, the Netherlands defence ministry said Monday.

The chopper was on its way to neighbouring island Curacao on Sunday afternoon when it came down 12 kilometres (seven miles) off the coast of Aruba, a Netherlands overseas territory, the ministry said.

"Two of the four team members (on board) were killed," said Rob Bauer, head of the Dutch armed forces, at an early-hours press conference in The Hague. "The two other team members are not seriously injured," he added, calling the incident "terrible news" and "a shock for everyone".

The cause of the crash was not immediately clear but a coast guard helicopter and Dutch military divers would try to find the aircraft's black box, he said.

However, the search would be made more difficult by strong winds, currents and large waves, Bauer cautioned, adding that an investigation would be opened.