An asylum-seeker boat believed to be carrying 200 people has capsized off remote Christmas Island with an unknown number of survivors, Australian authorities said.

The Australian Maritime Safety Authority (AMSA) said on Thursday that the ship issued a distress call mid-afternoon and capsized 200km of the Indian Ocean territory, some 2,600km from the Australian mainland.

Australian police said that early reports suggested up to 75 asylum seekers had died after the boat capsized en route from Sri Lanka.

"There is a capsized vessel 120 nautical miles north of Christmas Island, there's believed to be approximately 200 people on board," an AMSA spokeswoman told AFP news agency.

"We can confirm there are survivors but we can't confirm numbers at this stage," she said. "The Indonesian search and rescue authorities are co-ordinating the response."

'Details sketchy'

Al Jazeera's Andrew Thomas, reporting from Sydney, said: "Details at this point are still sketchy".

"Search and rescue teams from Indonesia and Australia are investigating reports that a second boat - possibly carrying another 100 asylum seekers - may also have gone down in the Indian Ocean.The Search and Rescue effort directed at the boat known to have capsized is being led by Indonesia with support from Australia.

"At least one Australian Defence Force vessel is now on the scene, picking up survivors. A second boat is en route. A cargo vessel - the WSA Dragon - was the first boat to arrive and is believed to have picked up survivors too," our correspondent said.

Australian Customs said a border patrol aircraft spotted the vessel in distress in Indonesia's search and rescue zone at about 0500 GMT and "it is believed up to 200 people could be on board".

Three merchant vessels and two Australian military ships had responded to a regional maritime alert and were on their way, and a fixed-wing P3 Orion aircraft was on the scene, according to AMSA.

A number of asylum boats have been intercepted in the area in the past 24 hours carrying more than 100 passengers, prompting Home Affairs Minister Jason Clare to issue a statement calling for an urgent political compromise.

"Let's remember what this is all about - 200 people died off the coast of Indonesia and another 11 died off the coast of Malaysia," Clare said in a statement earlier on Thursday, referring to previous recent accidents.

Series of accidents

So far this year 62 vessels carrying 4,484 boatpeople have been intercepted off Australia, an unprecedented number in a six-month period.

Arrivals have increased steadily since Canberra was forced to abandon a so-called "people swap" deal with Malaysia by the High Court last year and roll back its mandatory detention policy for boatpeople.

The government has had to release hundreds of asylum-seekers into the community while their applications are processed due to the strain on detention centres, the budget for which has now spiralled above $1 billion.

Though they come in relatively small numbers by global standards asylum-seekers are a sensitive political issue in Australia, dominating 2010 elections due to a record 6,555 arrivals.

Indonesia is a common transit point for those trying to reach Australia's Christmas Island, which is closer to Java than mainland Australia, but many of the overloaded, rickety vessels do not reach their destination.

In December, a boat carrying around 250 mostly Afghan and Iranian asylum-seekers sank in Indonesian waters on its way to Christmas Island, with only 47 surviving.

Some 50 refugees were killed in a shipwreck on the remote island's cliffs back in December 2010 when their leaky wooden vessel was dashed on the rocks.

Fifteen were children aged 10 years or younger, with one a baby just three months old.

Source: Al Jazeera and agencies