Recovery teams have narrowed the search area for AirAsia Flight 8501, hopeful they were closing in on the plane's crash site, with a total of 30 bodies and more debris recovered from the sea.

French and Singaporean investigators joined the hunt for the Airbus A320-200, which disappeared from radar during a storm Sunday en route from Indonesia's second city of Surabaya to Singapore with 162 people on board.

The search teams have deployed side-scan sonar equipment to survey the seabed and pinger locators to fine-tune their search for the plane's black boxes, crucial to determining the why the plane crash into the Java Sea off Borneo.

Rough weather has in recent days hampered the search for the plane's fuselage, which is believed to be in relatively shallow water of around 25-32 metres.

Search and rescue agency chief Bambang Soelistyo said the operation was focused on an area of 1575 square nautical miles -- a tenth of the size of Thursday's search -- with 29 ships and 17 aircraft engaged in the operation.

"There are two main tasks in this priority sector: first, to locate the biggest part of the plane's body," he told a press conference.

"The second task is to find the position of the black boxes, or flight recorders, which will be carried out by the KNKT (National Transportation Safety Committee) which start working today."

"Divers are already on standby at the navy ship Banda Aceh to dive on that priority area to locate the body of the plane," he said, voicing hope for a "significant result".

KNKT chief Tatang Kurniadi told AFP that 40 divers, including 20 deep sea experts, arrived Friday from Russia to help, along with two planes, one amphibious.

Extreme weather

The search is now focused on an area of 45 by 35 nautical miles centred about 75 nautical miles southwest of Pangkalan Bun, a town in Central Kalimantan on Borneo.

With the search area narrowing, Indonesian official S.B. Supriyadi said they were pressing on despite rough conditions, with high winds and 3-4 metre waves.

"The search is still proceeding in systematic way, despite the extreme weather," he told a press conference.

He said ships equipped with sonar may search through the night, but high waves were hampering the use of equipment to find the black boxes.

Two South Korean Orion surveillance planes Friday spotted six bodies, Indonesian air force spokesman Hadi Tjahjanto said in a press release.

"After sweeping the area for more than two hours, at 11:58 the (Orions) found three bodies sitting in one row," he said, and another three just minutes later.

They informed warships by radio and fired flares to indicate the location for retrieval, he said.

More victims identified

Relatives were preparing to hold funerals after three more victims were identified, including flight attendant Khairunisa Haidar Fauzi, who had recently posted an Instagram picture with the message "I love you from 38,000 ft" for her boyfriend.

"I'm arriving in Surabaya to take Nisa (Fauzi) home to Palembang. I cannot describe how I feel. There are no words," AirAsia chief Tony Fernandes tweeted.

Also named was Grayson Herbert Linaksita, 11, who was travelling with his parents and 12-year-old sister for a holiday.

His great-uncle Bagyono Linaksita, 73, told AFP was dreading breaking the news to the children's grandmother, who was on holiday in the Czech Republic.

"She doted on her two grandchildren and would send and fetch them from school every day," he said.

"We have not told her the news that the whole family had died in a plane crash. Grayson was her favourite grandchild. She will certainly faint."

A crisis centre for identifying the victims has been set up at a police hospital in Surabaya with facilities to store 150 bodies.

Before take-off, the pilot of Flight 8501 had asked for permission to fly at a higher altitude to avoid a storm. But his request was not approved due to other planes above him on the popular route, according to AirNav, Indonesia's air traffic control.

In his last communication, Captain Iriyanto, an experienced former air force pilot, said he wanted to change course to avoid the menacing storm system. Then all contact was lost, about 40 minutes after the plane had taken off.

Of the 162 passengers and crew on board, 155 were Indonesian, with three South Koreans, one Singaporean, one Malaysian, one Briton and a Frenchman -- co-pilot Remi Plesel.

The plane was operated by AirAsia Indonesia, a unit of Malaysia-based AirAsia, which previously had a solid safety record.

The crash came at the end of a disastrous year for Malaysian air travel.

After the disappearance of Flight MH370 in March, en route from Kuala Lumpur to Beijing with 239 passengers and crew, another Malaysia Airlines flight -- MH17 -- was shot down over Ukraine in July, killing all 298 on board.