A boat packed with 66 asylum-seekers, thought to be from Sri Lanka, has managed to evade detection by border patrols and arrived at a port on the Australian mainland, officials say.

The boat was spotted within the harbour limits of Geraldton in Western Australia, more than 2000km south of Christmas Island where asylum seekers coming to Australia are usually intercepted.

The vessel arrived about 12 noon on Tuesday.

“Customs and Border Protection have advised a suspected irregular entry vessel arrived within the harbour limits of Geraldton this afternoon,” Australia’s Home Affairs Minister Jason Clare confirmed.

“Initial indications suggest there are 66 people on board.”

Locals were stunned as the crowded fishing boat approached. It is thought it came from Sri Lanka and had been at sea for around six weeks.

Customs officials have taken the vessel ashore, and a temporary screening centre has been set up to process the arrivals.

Mayor of Greater Geraldton, Ian Carpenter said he’s very surprised the boat made it so far.

“As far as I’m aware, this is the first time it’s happened.  You wonder how these people got through without being detected,” he said.

“If these people can get through 2000km of water, I guess others could as well.”

It is highly out of the ordinary for an asylum seeker boat to travel this far south, with most asylum seeker boats arriving off the coast of Western Australia, near Christmas Island, thousands of kilometres north.

Geraldton is approximately 400 kilometres north of Perth.

- Agencies