A boat carrying 67 Tamil asylum seekers has arrived undetected at the Cocos Islands.

The boat was 200 metres from the Cocos Islands when four of the men onboard swam ashore.

Local resident Jack O'Donnell, who has a beachfront house, says he spotted the boat just after 8:00 am local time..

"About 10 minutes later four of the refugees, they're Tamils, swam with life jackets through the surf," he said.

Mr O'Donnell says one man, who spoke broken English, said the people on board were exhausted and in need of food.
"It was obviously crowded with bodies," he said.

"We were just worried that they might try and traverse the surf which would be dangerous, well, it would be catastrophic because it's jagged reef."
Mr O'Donnell says he alerted police who showed up and spoke to the four men.

It is understood the boat has been towed to the island's lagoon.

The asylum seekers have since been taken into custody and will be transferred to Christmas Island.

Opposition Customs and Border Protection spokesman Michael Keenan says he is not surprised the boat arrived undetected because there are too many for Customs vessels to deal with.

"These are very hardworking men and women who are doing a very difficult job but unfortunately they're mopping up the consequences of Labor's failed polices," he said.

"It's clearly increasingly difficult to intercept those vessels before they get to Australia."

Overnight, a boat carrying 28 asylum seekers was intercepted west of the Cocos Islands but it is believed the two boats are different.

Meanwhile, Australian authorities have intercepted an asylum seeker boat north of Christmas Island.

It is understood there are 43 passengers and two crew on board.

The group has been transferred to Christmas Island for health, security and identity checks. (Source: AbC News Australia)