Australia has called off a major air-and-sea search for survivors from a boat carrying at least 55 asylum-seekers which disappeared suddenly off a remote Indian Ocean territory.
Officials late Sunday halted the search for the vessel off Christmas Island -- which was seen before it went down carrying men, women and children -- after failing to find anyone alive.
Up to 13 bodies were spotted in the water during the extensive search. But Customs said staff were occupied with a number of "high-priority operations" in Australian waters and would not be able to recover the bodies on Monday.
"All Border Protection Command vessels and aircraft have been released from the search for survivors," Customs said in a statement.
"No attempts to recover the deceased are being made today."
Customs said border protection vessels and aircraft "are currently involved in a range of high-priority operations in waters near Christmas Island and elsewhere".
"Our priority is responding to other vessels which may require assistance, and preventing any further loss of life," the statement said.
"If operations permit, Border Protection Command will, where it remains feasible and without further risk to life, endeavour to recover any bodies which may be relocated."
The stricken vessel was initially spotted by a Customs plane off Christmas Island on Wednesday. But when a boat attempted to intercept it the following day it had vanished.
Thirteen bodies and an upturned hull along with other debris were subsequently spotted.
The number of people attempting to reach Australia by boat has hit record levels, with the figure expected to top 25,000 in the 12 months to June 30 despite punitive "no advantage" policies banishing refugees to remote Pacific detention camps.
There was no immediate information about the nationality of the passengers on the capsized boat. But Myanmar, Iraq, Afghanistan and Sri Lanka are common source countries for asylum-seekers arriving in Australia via people-smuggling boats, mostly from Indonesia.
Hundreds of refugees have died in asylum-seeker boat accidents in recent years, including a vessel which disappeared without trace in the Sunda Strait in April with 72 on board. Last month 28 life jackets washed up on the Cocos Islands in the Indian Ocean, prompting fears of more drownings.
The latest tragedy has prompted calls for an investigation into the timing of the search. The operation began as other boats were arriving, including one carrying 78 people which sought help from authorities.
"If there's an issue of resource then that needs to be public," Ian Rintoul from the Refugees Action Coalition told the ABC.
Rintoul said until the government put policies in place to process asylum-seekers in Indonesia, people would continue to board boats.
"If its policies are pushing people onto boats, then the least it can do, if it's not willing to escort boats... is make sure that there are the resources available so we don't see the loss of life at sea," he said.
The United Nations refugee agency expressed its "deep concern" at the latest deaths.
"The reality of yet more lives lost on the high seas highlights the dangers of these journeys and the need to redouble efforts to find effective and humane regional solutions," the UNHCR said in a statement.