Australia ordered an investigation on Wednesday into how an asylum-seeker boat managed to reach one of the country's busiest ports undetected and warned that those on board may be flown back home. The rickety vessel carrying 66 Sri Lankans was spotted on Tuesday within the harbour limits of Geraldton in Western Australia, 425km north of Perth. The state's Premier Colin Barnett called it "a serious, unprecedented and unacceptable breach of Australia's border security" - the first such boat to reach the Australian mainland in five years. Home Affairs Minister Jason Clare said most vessels opted for the shortest route to Australia, which took them to the country's Indian Ocean territory of Christmas Island, 2,000km to the north-west of Geraldton.