Authorities are understood to be following the road map laid out by the search for Air France flight 447, meaning the next stage will likely involve using towed sonar scanners and remotely operated vehicles.

However, they are waiting until the Bluefin-21 finishes its search of the narrow area  - which is expected in the next week - before deciding what to do next. Australian authorities will need to consult closely with Malaysia before embarking on the next phase.

Considerable international determination remains to keep the search going, sources say. China, in particular - 153 of whose nationals were on board the plane - is treating the matter as an important one of national prestige.

The international search being coordinated by former Chief of the Defence Force, Angus Houston, is focused on a patch of ocean bed about 300 square kilometres that is being scoured by the Bluefin-21. The search area is based on the electronic pings believed to be from the MH370's black box that were heard by an Australian Navy ship.

By Monday, the autonomous underwater vehicle had covered more than two-thirds of the search area, meaning it is likely to be done within days.

A spokeswoman for Air Chief Marshal (retired) Houston's joint agency search team said no requests had been made for additional equipment.

"It is important that Bluefin-21’s search activity is completed so we can either confirm or discount the focused underwater area as the final resting place of MH370," she said. "At this point, no decision about a transition to the next phase has been made."

However, it is understood that preliminary enquiries have been made on the assumption that Bluefin-21 may come up empty-handed. A source said: "The next step is, what if we don't find anything?"

With a broadened search area, it is likely the next stage would use side-scan sonar devices towed by a ship. Like the Bluefin-21, these use sonar to build up a map of the sea floor but can cover a larger area than the underwater drone.

A remotely operated vehicle is also likely to be sought to help with the next stage.

These were the types of equipment used in the search for flight AF447, which crashed into the Atlantic Ocean in June 2009. That search is now regarded as a template for such operations, though it took nearly two years for the black boxes to be recovered.

It is understood that Beijing is continuing to apply considerable diplomatic pressure to ensure the search continues and is successful.