Story highlights The ship overturns midway between Australia and Indonesia

Vessels are on the scene in hope of rescuing survivors

Authorities don't know exactly how many were onboard because they board illegally, an official says

A ship carrying about 200 people capsized in the waters between Australia and Indonesia, rescue officials in both countries said Thursday.

A merchant ship was diverted to the scene and is taking on survivors, said Jo Meehan of the Australian Marine Safety Authority.

An Australian naval vessel has also arrived on the scene and is preparing to take on survivors. In addition, an Australian Defence Forces aircraft at the location has dropped four life craft capable of carrying a total of 60 people, she said.

Indonesia said it is sending two warships to assist Australian rescue efforts.

"We never know the exact number of people onboard as they get onboard illegally," said Gagah Prakoso, a spokesman for Indonesia's Search and Rescue Agency.

The vessel is 110 nautical miles northwest of Christmas Island. The Australian territory is closer to Indonesia and in the latter's designated search-and-rescue area, said Susan Usher of the Western Australian Police.

She would not characterize the people aboard the vessel nor did she know their fate.

Christmas Island has been the scene of another recent boat capsizing.

At least 28 people died in December 2010 when a boat carrying asylum seekers crashed into cliffs near the coast of the island.

Most of the people on the boat were from Iran and Iraq, a rescue worker said at the time.