Australian Prime Minister Kevin Rudd promised to leave “no stone unturned” in efforts to look for the six mining executives, including a billionaire magnate, whose plane went missing over Cameroon.

Dubbing the situation as “deeply concerning,” Mr. Rudd said the Australian government was working with local authorities and will spare no effort in the search.

The six men, including one of Australia’s richest men Ken Talbot, were among 11 people on board the plane chartered by Perth firm Sundance Resources when it went missing over Cameroon on Saturday.

Talbot is a non-executive director of iron-ore miner Sundance, with estimated wealth of 965 million dollars ($ 840 million), according to BRW business magazine’s latest rich list.

An aerial search of the plane’s route overnight failed to turn up any sign of the missing plane.

The twin-engined aircraft disappeared about halfway into its hour-long flight between Cameroon’s capital Yaounde and the town of Yangadou in neighbouring Congo.

Cameroon sent a Hercules C-130 and two smaller aircraft to scour the route taken by the plane, and Cameroon president Paul Biya has set up a crisis panel to coordinate the search.

The search operation was called off for the night, but Foreign Minister Stephen Smith said it will resume in the morning local time, weather permitting.

“All of our diplomatic and consular resources are being dedicated to this,” Mr. Rudd said.

“We are working with the local authorities. We will leave literally no stone unturned in our efforts to try and help what is a concerning set of developments for these Australians,” Mr. Rudd said, according to an ABC report.

Mr. Smith said the search operation was focusing on the border area between the two countries.

He said Australia was working closely with local authorities and he was in touch with Australia’s high commissioner to Nigeria, who is on the ground.

Mr. Smith said the plane made contact with ground control twice before it disappeared.

“The advice I have is both of those contacts were standard identification and procedural contacts,” he said.

Mr. Smith said the flight should have taken about an hour in duration.

“We will await the outcome of the search. In the meantime, we will continue to give consular assistance to the company and to the family members,” he said.

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