A helicopter crashed south of Kuala Lumpur Saturday killing all six people on board, including Prime Minister Najib Razak's 'Chief of Staff' and a former ambassador to the United States.

The helicopter went down in a rubber plantation in the town of Semenyih with Najib's principal private secretary, Azlin Alias, aboard.

Also among the dead was Jamaluddin Jarjis, a lawmaker and a senior member of Najib's political party UMNO. Jamaluddin was a former Malaysian ambassador to the United States.

"I am personally grief-struck. Jamaluddin Jarjis was my friend of many years and no truer friend could I have," Najib said in a statement.

"Azlin Alias was my Chief of Staff and a truly outstanding government servant. The contributions of these two men to the government, to UMNO and to Malaysia were very significant."

Najib added that he had ordered an investigation into the cause of the crash, saying that "no stone will be left unturned."

Transport Minister Liow Tiong Lai said in a separate statement that all six bodies had been recovered and sent to a hospital in the capital Kuala Lumpur.

"This is indeed a great loss and my thoughts and prayers are with their families and the families of the other victims during this tragic time," the minister said.

An eyewitness told Malaysia's official Bernama news agency that the helicopter "exploded in mid-air" during heavy rain.

"Then, the debris, tail and blades were thrown all over the place," the eyewitness, Roslan Harun, was quoted as saying.