Weather worsening in MH370 search zone

The multi-national hunt for the missing Malaysia Airlines flight is set to be hampered by the weather again, with predictions of gales and thunderstorms in the search zone.

The search for wreckage of the crashed Boeing 777 resumed on Wednesday after the weather improved, with Chinese ships and Korean planes joining the mission over a vast stretch of the Indian Ocean, about 2000km southwest of Perth.

Six countries are now involved in the operation - Australia, New Zealand, the United States, Japan, China and South Korea - after Flight MH370 vanished on March 8, with 239 passengers on board, including six Australians.

The US Navy has sent a device to Perth to help find the jet's black box of flight and cockpit voice data, along with a robotic underwater vehicle.

But its deployment may have to be delayed, with warnings of potentially damaging weather conditions in the southern Indian Ocean on Thursday.

"We've mentioned the possibility of gale force winds and thunderstorms. These conditions are markedly worse than those of today," a Bureau of Meteorology spokesman told AAP.

"At the moment, the forecast is suggesting poor conditions tomorrow."

The Australian Maritime Safety Authority (AMSA) will make a determination on the search activity later on Wednesday.