A 16-year-old girl trying to sail solo around the world was adrift in the southern Indian Ocean today awaiting rescue after 30ft waves wrecked her yacht.

Following a desperate emergency call then tense 20 hours of silence, a search plane launched from Australia's west coast made radio contact with Abby Sunderland.

The boat's mast was broken - ruining satellite phone reception - and was dragging with the sail in the ocean, said the Australia Maritime Safety Authority which chartered a commercial jet for the search.

But the keel was intact, the yacht was not taking on water and Abby was equipped for the conditions, a spokesman said.

"The aircraft (crew) spoke to her. They told her help was on the way and she sounds like she's in good health.

"She's going to hang in there until a vessel can get to her," probably on Saturday, he said.

A lifelong sailor, Abby had begun her journey trying to be the youngest person to sail solo, non-stop around the world and continued her trip after mechanical failures dashed that dream.

Abby told searchers that she was doing fine with a space heater and at least two weeks' worth of food.

Three rescue boats from the island of Reunion, off Madagascar, are expected to reach her tomorrow.

She had made several broken calls to her family in California, and reported her yacht was being tossed by 30ft waves. An hour after her last call ended, her emergency beacons began signalling.

The observers aboard the search plane - a chartered Qantas Airbus A330 jet that left Perth - spoke with her by close-range VHF marine radio.

Renowned Australian round-the-world sailor Ian Kiernan said Abby should not have been in the southern Indian Ocean during the current southern hemisphere winter.

"Abby would be going through a very difficult time with mountainous seas and essentially hurricane-force winds," he said.

Conditions can quickly become perilous for any sailor exposed to the elements in that part of the world.

Abby - whose father is a shipwright and has a yacht management company - set sail from Los Angeles in her boat, Wild Eyes, on January 23 in an attempt to become the youngest person to sail around the world alone without stopping. Her brother Zac briefly held the record in 2009.

She soon ran into equipment problems and had to stop for repairs. She gave up the goal of setting the record in April, but continued on.

On May 15, Australian 16-year-old Jessica Watson claimed the record after completing a 23,000-mile circumnavigation in 210 days.