A ship involved with the search for the missing Malaysia Airlines Flight 370 is being fitted with a drone to examine several sonar contacts on the remote seabed west of Australia.

The Australian Transport Safety Bureau, which is leading the search for the Boeing 777, said on Wednesday none of the sonar contacts are characteristic of a typical aircraft debris field, but some do exhibit man-made properties and must be investigated.

Officials previously said more than 20 sonar contacts picked up by crews in recent months require closer examination by a sonar-equipped water drone. They are between 2,700km and 1,900km from the Australian port of Fremantle where the search ships are based.

The Chinese vessel, Dong Hai Jiu 101 is being fitted with a video camera-equipped remotely operated vehicle that will scrutinise the sonar contacts. Poor weather conditions during the southern hemisphere winter prevented the drone from being deployed before now.

Crews have picked up hundreds of sonar contacts of interest during the two-year hunt for MH370, which vanished on 8 March 2014, during a flight from Kuala Lumpur to Beijing with 239 people on board.

The contacts are grouped into three classification levels, with those labelled "classification 1" considered most likely to have come from the aircraft.

None of the recent sonar contacts the drone will investigate are classification 1. Only two have fitted into that category during the search - one was an old ship wreck and the other was a rock field.

An underwater search of 120,000 sq km of seabed in the southern Indian Ocean, which is believed to cover the most likely area for a crash site, is almost complete - without any trace of the plane being found.

In pictures: Missing Malaysia Airlines flight MH370 Show all 30 1 /30 In pictures: Missing Malaysia Airlines flight MH370 In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives A family member of a passenger aboard the missing Malaysia Airlines flight MH370 burns incense as he prays at Yonghegong Lama Temple in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives Family members of passengers aboard the missing Malaysia Airlines flight MH370 burn incense to pray at Yonghegong Lama Temple in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives A family member of a passenger aboard the missing Malaysia Airlines flight MH370 comforts another relative as they gather to pray at Yonghegong Lama Temple in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives Relatives of passengers on missing Malaysia Airlines flight MH370 cry as they gather at the Lama Temple in Beijing. Chinese relatives marked 100 days since the plane went missing on a flight from Kuala Lumpur, Malaysia to Beijing by offering prayers and burning incense at the buddhist temple In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives Relatives of passengers on missing Malaysia Airlines flight MH370 offer prayers at the Lama Temple in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives A Chinese relative of passengers of Malaysia Airlines flight MH370 prays at the Lama Temple in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives Chinese relatives of passengers of Malaysia Airlines flight MH370 hold incense sticks and pray at the Lama Temple in Beijing In pictures: Missing Malaysia Airlines flight MH370 Malaysian relatives Intan Maizura Othman (34) wife of MH370 fligh attendant Hazrin Hasnan holds placard during an event to remember the 100th day of the missing crews and passengers of Malaysian Airlines plane MH370 in Damansara, Selangor In pictures: Missing Malaysia Airlines flight MH370 Malaysian relatives A young relative tries to stick paper planes on a board during an event to remember the 100th day of the missing crews and passengers of Malaysian Airlines plane MH370 in Damansara, Selangor In pictures: Missing Malaysia Airlines flight MH370 Malaysian relatives Pictures of crews and passengers is displayed during an event to remember the 100th day of the missing crews and passengers of Malaysian Airlines plane MH370 in Damansara, Selangor In pictures: Missing Malaysia Airlines flight MH370 Search for flight MH370 The Phoenix International Autonomous Underwater Vehicle (AUV) Artemis is craned over the side of Australian Defence Vessel Ocean Shield in the search for missing Malaysia Airlines flight MH 370. Twenty-six nations have been involved in the search for Malaysia Airlines Flight MH370 since it disappeared more than a month ago In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives Chinese women, relatives of Chinese passengers onboard the Malaysia Airlines MH370 cry as they wait for Malaysia embassy staff to meet them outside the Malaysia embassy in Beijing. About 50 relatives of Chinese passengers on the plane continued a sit-in protest outside the Malaysian Embassy after officials failed to show up to update them on the search In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives A relative of Chinese passengers onboard the Malaysia Airlines MH370 speaks to media as he and others wait for Malaysia embassy staff to meet them outside the Malaysia embassy in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives Relatives of Chinese passengers onboard the Malaysia Airlines MH370 push through a police line to march to the Malaysian embassy from a hotel in Beijing. Angry relatives who had been waiting for more than 8 hours in vain for a Malaysia embassy representative to attend their daily meeting marched to the Malaysia embassy and protested through the night In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives Chinese police men try to prevent relatives of Chinese passengers onboard the Malaysia Airlines MH370 from marching to the Malaysian embassy from a hotel in Beijing In pictures: Missing Malaysia Airlines flight MH370 Search for flight MH370 Flying Officer Elizabeth Vonfinster, an Air Combat Officer with No. 2 Squadron sits at her station aboard the RAAF E-7A Wedgetail Airborne Early Warning and Control (AEW&C) aircraft during its return from another mission in the search for the missing Malaysia Airlines Flight MH370 in the southern Indian Ocean In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives Wen Wanchang, whose son was on board the Malaysia Airlines Flight 370, cries as he pleads with Malaysian embassy representative Bala Chandran Tharman for answers during a meeting in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives A relative of a passenger aboard Malaysia Airlines flight MH370 is carried by medical personnel and policemen after collapsing during a briefing Lido Hotel in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives Relatives of Chinese passengers onboard the Malaysia Airlines Flight 370, cry during a meeting in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives A relative of Chinese passengers onboard the Malaysia Airlines Flight 370, cries as she asks for answers during a meeting with Malaysia embassy and Malaysia Airlines representatives in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives A Chinese relative (C) of passengers on the missing Malaysia Airlines flight MH370 reacts as he attends a meeting at the Metro Park Hotel in Beijing In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives A relative of Chinese passengers onboard the Malaysia Airlines Flight 370, demands answers from Malaysian representatives at a meeting in Beijing. Relatives chanted slogans and shouted protests against the lack of meaning answers from Malaysian officials and Malaysia Airlines representatives In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives A relative of a passenger aboard Malaysia Airlines flight MH370 cries as she speaks to Malaysian representatives during a briefing at Lido Hotel in Beijing. A tropical cyclone was threatening to hamper the search for a missing Malaysian jetliner in a remote stretch of the Indian Ocean, as a submarine drone neared the end of its mission scouring the sea bed with still no sign of wreckage In pictures: Missing Malaysia Airlines flight MH370 Chinese relatives A Chinese relative of passengers onboard missing Malaysia Airlines (MAS) flight MH370 reacts in front of journalists as she arrives during a briefing at a hotel in Kuala Lumpur. The effort to find missing flight MH370 is at a "very critical juncture", Malaysia's transport minister said as authorities mull whether to reassess a challenging search of the Indian Ocean seabed that has so far found nothing In pictures: Missing Malaysia Airlines flight MH370 Search for flight MH370 Commander James Lybrand, Mission Commander ADV Ocean Shield (L) and Chris "Sharkie" Moore, Phoenix team leader, watch the launching of the Phoenix International Autonomous Underwater Vehicle (AUV) Artemis as it is craned over the side of Australian Defense Vessel Ocean Shield before launching it in to the southern Indian Ocean in the search of the missing Malaysia Airlines Flight 370 In pictures: Missing Malaysia Airlines flight MH370 Search for flight MH370 The Phoenix International Autonomous Underwater Vehicle (AUV) Artemis is craned over the side of Australian Defence Vessel Ocean Shield in the search for missing Malaysia Airlines flight MH 370 In pictures: Missing Malaysia Airlines flight MH370 Search for flight MH370 Leading Seaman, Boatswain's Mate, William Sharkey searching for debris on a rigid hull inflatable boat at sea in the Southern Indian Ocean In pictures: Missing Malaysia Airlines flight MH370 Search for flight MH370 Boatswain's Mate, Able Seaman Morgan Macdonald (L) observing markers from a Royal New Zealand Air Force (RNZAF) P3K Orion at sea in the Southern Indian Ocean. An oil slick in the Indian Ocean is not from missing Malaysia Airlines flight MH370, officials said when insisting underwater search efforts would be 'pursued to their completion' In pictures: Missing Malaysia Airlines flight MH370 Search for flight MH370 HMAS Perth transiting through the Southern Indian Ocean as an Orion P-3K of the Royal New Zealand Air Force searches for debris for missing Malaysia Airlines flight MH 370 in the southern Indian Ocean In pictures: Missing Malaysia Airlines flight MH370 Search for flight MH370 Craig Turner from Phoenix International monitoring the Artemis' depth and speed as the Autonomous Underwater Vehicle scans the ocean floor for missing Malaysia Airlines flight MH 370 in the southern Indian Ocean

Malaysia, China and Australia agreed in July that the search in the southern Indian Ocean would be suspended after the current search site has been thoroughly examined with deep sea sonar equipment in the absence of credible new evidence that identified the plane’s location.

Officials previously said the search would be finished by December, but on Wednesday, the transport bureau said it is now likely to take until January or February to complete, due disruption from poor winter weather.

Last month, investigators cast doubt on the discovery of "fire-damaged" debris washed up on Madagascar, which were seen as possible evidence to the cause of the crash.

Officials at the Australian Transport Safety Bureau are still yet to determine whether the five items of debris came from the missing Boeing 777. But said a preliminary investigation showed at least two of the pieces, panels of fiberglass honeycomb, were discoloured naturally as a result of resin in the material, not exposure to fire or heat.