A one-month-old baby in Vanuatu has become the first person in the world to be immunised using vaccines delivered by a commercial drone, the United Nations says, raising hopes that the method could save lives in other far-flung areas.

The drone flew for 25 minutes across 40km of mountainous terrain to get to the Cook's Bay area on the island of Erromango, which would otherwise have taken hours to reach on foot or by boat.

Vanuatu is the world's first government to contract a commercial drone company to deliver vaccines, according to the UN children agency, UNICEF, which called the successful trial on Tuesday a "big leap for global health".

A nurse picked up the vaccines, including those that immunise against polio and tuberculosis, and administered them to 13 children, including the one-year-old baby, and five pregnant mothers.

"It is very innovative. I hope it will extend to a wider region," said Gina Dehinavanua, of humanitarian agency CARE International, on Wednesday.

"It will help our kids and ensure those aged between zero and five have all the necessary vaccines to grow up as a child," she told the Thomson Reuters Foundation by phone from Vanuatu's capital, Port Vila.

The Pacific island nation, with about 280,000 people spread across roughly 80 islands, is one of the world's poorest countries. Only about a third of its inhabited islands have airfields and proper roads.

Out of every 1,000 babies born in Vanuatu, 28 die before they reach the age of five, according to UNICEF data from 2016, while only one in five children is fully immunised.

Vaccines are difficult to transport as they need to be kept at specific temperatures. During the drone flight, they were kept in Styrofoam boxes with ice-packs and a temperature sensor.

"With the world still struggling to immunise the hardest to reach children, drone technologies can be a game changer for bridging that last mile to reach every child," UNICEF executive director Henrietta Fore said in a statement.

Drone deliveries will be tested in more villages across the archipelago before Vanuatu's government decides if the method will be used more widely.