The Pacific national airline is creating a wider row on its aircrafts for passengers who weigh more than 286 pounds (130 kilograms). Samoa has one of the world's highest rates of obesity.

The airline's head, Chris Langton, said the XL row would be extended by 12 to 14 inches and the changes would be introduced by the end of the week.

"Once you're up around that sort of [weight] ... a traditional seat on any airline is going to be uncomfortable," he told ABC News.

"Quite often the access is difficult, and even the space between the seats is enough that even when you've squeezed into the seats there's no room for your legs. That's where the XL has come in – we do it with shirts and clothing and other things where we have different standard sizes."

Passengers on Samoa Air do not pay for a seat but pay a fixed price per kilogram, which varies according to the length of the route. The passengers nominate their weight and are then measured, along with their baggage, on scales at the airport. The rates range from about $1 (64p) a kilogram on the airline's shortest domestic route to about $4.16 per kilogram for travel from Samoa to the neighbouring nation of American Samoa.

Mr Langton said he believed other international airlines would eventually start charging by weight and modifying their aircraft to accommodate the changing shapes of their passengers.

"The airline industry is going to have to do that – we're going to have to provide a range of seats categorised in terms of weight and maybe some other indexes like height," he said.

"So when people travel they can give us those indicators and we can allocate them to an appropriate seat."

Airlines in Australia this week ruled out imposing a "size surcharge" on obese passengers despite acknowledging the extra fuel costs of transporting larger people.

"We recommend passengers who cannot sit with both arm rests down consider a second seat for their comfort and safety," said a spokesman for Jetstar, the budget airline owned by Qantas.

Virgin Australia said obesity was a "big issue" and it sometimes weighed individual passengers to assess the weight of the aircraft.

"It's something you've got to start to watch very carefully but the last thing we want to do is make customers uncomfortable," said the airline's boss, John Borghetti.