KUALA LUMPUR (AFP) - Families of those lost on flight MH370 pleaded on Thursday (July 21) for authorities to continue hunting for the Malaysia Airlines jet on the eve of a meeting that could decide how much longer the frustrating deep-sea search continues.

The appeal by an international group of MH370 next-of-kin, Voice 370, called on "Malaysia, Australia and China not to abandon the search" if the current zone being trawled for the wreckage is found to be empty, a statement by the group said.

"If for any reason an immediate extension of search activities cannot be carried out, then the search should merely be suspended, not abandoned in totality," Voice 370 said.

The statement was released at a press conference in Kuala Lumpur in which a dozen grim-faced next-of-kin held up placards pleading with authorities not to give up the search.

The Boeing 777 vanished March 8, 2014, en route from Kuala Lumpur to Beijing with 239 people aboard, mostly Chinese nationals, in what remains one of the greatest mysteries in aviation history.

The Australian-led operation is scouring the seafloor within a 120,000 sq km belt of remote Indian Ocean where authorities believe the passenger jet went down.

The Voice 370 statement was issued as as transport ministers from Australia, China and Malaysia prepared for a meeting on Friday that may dictate how much longer the search continues.

That area currently being surveyed is expected to be fully searched possibly in the next few weeks.

The three countries have said the hugely expensive high-tech sonar operation far off western Australia will not be further expanded without "credible" new evidence pointing to a crash site.

Australian Transport Minister Darren Chester said this week that Friday's meeting in Malaysia would be an opportunity to "discuss next steps" as the search nears completion.

Many families are sceptical the search is in the right place, and Voice 370 has previously called for a full public double-checking of data used to determine the suspected crash region.

Its statement on Thursday also repeated calls for a concerted international effort to find and study more debris in the western Indian Ocean.

Several pieces of debris that apparently drifted thousands of kilometres towards the African coast have been identified as definitely or probably from the Boeing 777.

Those finds have confirmed the plane went down but have so far shed no light on the cause of the crash.