The investigation is expected to reveal how the boat had reached Geraldton in Western Australia without being detected by the Navy, Naval spokesman Kosala Warnakulasuriya said.
The boat was spotted on Tuesday within the harbour limits of Geraldton in Western Australia, more than 2,000 kilometres south of Australia's Indian Ocean territory of Christmas Island. It was the first asylum boat to reach the Australian mainland.
Reacting to the arrival, the Australian authorities have indicated the asylum-seekers would be sent home by air.
He was stressing that they were economic migrants and debunked the theory that people resort to the risky boat ride to reach Australia due to human rights violations in his country.
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In recent months, Sri Lankan Navy had intercepted several boats within the Sri Lankan waters carrying several hundreds of would be asylum-seekers to Australia.
Faced with recurring arrivals of Sri Lankan asylum-seekers since 2010, the Australians set up an off shore processing centre last August in the Pacific island of Nauru and Christmas Islands.