Eight Australians are among 19 volunteer teachers missing in Vanuatu, five days after Cyclone Pam tore through the Pacific nation.
The volunteers were in Vanuatu with Lattitude Global Volunteering, the international youth development charity confirmed on Wednesday.
A spokesperson for Lattitude said the organisation was working with the Department of Foreign Affairs and Trade and local authorities on the ground to try to find the missing volunteers.
A DFAT spokesperson said locating the missing group remained its top priority.
"Consular officials have not yet located the group of young Australian volunteers on Pentecost Island and they remain our highest immediate consular priority," the spokesperson said.
All 19 were undertaking voluntary teaching placements on the eastern islands of Pentecost and Ambae when the cyclone struck.
Zoe Marshall, of Canberra, and South Australian Ally Trueman, both 18, are believed to have been volunteering with the group.
The cyclone devastated Vanuatu on Friday, claiming at least 24 lives.
Ms Marshall's mother, Alison Abernethy, said she last heard from her daughter on Thursday morning via text message as the teenager bunkered down in anticipation of the storm.
She is choosing to believe her daughter is helping villagers on Pentecost Island clear the cyclone damage.
"Sorry for early text but don't know when phone will work," Ms Marshall's last text read. "We've got a cat 5 warning, should hit us tonight. Should be all good. I love you more than most things."
Ms Abernethy, her husband, Rob Marshall, and Ms Marshall's brother, Angus, 16, heard from her nearly every day prior to the storm.
Ms Abernethy said the silence had been "dreadful, really, really horrible".
She said the island had intermittent reception and no internet connection prior to the storm and was now completely cut off.
"[Zoe] had been advised the storm had been upgraded to a category 5 and that she did not expect her phone to work. She didn't know when her phone would work again," Ms Abernethy said.
"We'd been texting back and forward during the week. She was telling me they were prepared for the cyclone and had reinforced the rooves and packed away all the school materials and prepared food and water – she was pretty relaxed, she was telling me about how it was all good."
An RAAF reconnaissance flight has given the family hope.
"The damage to the area wasn't as bad as say Port Vila or the southern provinces," Ms Abernethy said.
"That gave us a lot of hope but what that means is the relief effort has been focused on those other areas. There really isn't any information on Pentecost because nobody's going there."
But this could change with a medical boat leaving for the remote island on Tuesday night.
"They've got the details of Zoe and the other volunteers," Ms Abernethy said. "We're hoping they might get word to them – they've got a satellite phone."
Ms Abernethy said she had heard World Vision was trying to send a plane to the island but could not confirm this with DFAT.
Ms Mitchell deferred an engineering place at the University of NSW and left for Vanuatu on February 9 for the five-month program, teaching school children in grades 1, 2, 5 and 6.
"She's been interested in helping people and doing good things since she was a little kid," Ms Abernethy said.
DFAT said consular staff in Vanuatu were making every effort to contact and assist Australians in the country.
"Aerial surveillance has been undertaken to locate Australians, however communications are out and airstrips are damaged on many islands, so contact and travel to these areas is very difficult," he said.
"Consular staff in Australia are in contact with families who have concerns for Australians in Vanuatu."
with Su-Lin Tan
