Bainimarama said he had the support of every Fijian in expressing sympathy for the loss of life and devastation caused by the bushfires, Radio New Zealand International reported.
"Our prayers are with the families who have suffered from the loss of their loved ones and their homes, businesses and property. I express great sympathy for the terrible loss of livestock and wildlife, and threats to native and endemic flora and fauna."
Bainimarama also saluted the "extraordinary bravery" of the thousands of men and women - especially the volunteers of the Rural Fire Service - who were "placing their lives on the line to protect their fellow Australians".
Bainimarama said Fiji would never forget the Australians, who helped his country recover from Cyclone Winston four years ago, and Fiji offered its assistance to Australia in any way it could.
"We count the Australian people as being among our closest friends and will always stand shoulder to shoulder with you."
Vanuatu's government will donate about $175,000 to the Rural Fire Service of Australia.
Acting Prime Minister Jotham Napat announced the donation on Sunday while expressing sympathy for Australia as it continues to suffer horrific bush fires, Radio New Zealand International reported.
The Vanuatu Daily Post reports Napat saying Vanuatu had "watched in awe" as volunteer rural fire services had given up their holidays to battle the crisis.
"It demonstrates the true Australian spirit and one which we are very proud of, as your friend and neighbour," he said.
His government was giving whatever assistance it could, he said, like Australia had always done for Vanuatu in times of need.
Napat also called on Ni-Vanuatu of all denominations to keep Australia in their prayers: "Australia will remain in our prayers. I encourage all churches in Vanuatu to remember our friends in their services."