A major United Nations conference on small island nations began in Samoa on Monday, with the emphasis on helping them survive the pressing challenge posed by climate change.

Some 3,000 delegates are attending the UN Small Island Developing States meeting, making it the largest event ever staged in the tiny Pacific nation of about 200,000 people.

UN Secretary General Ban Ki-moon said the conference, which ends Thursday, was a once-in-a-decade opportunity to promote sustainable development in countries such as Samoa, which are often described as on the front line of climate change.

"I know your country is facing a lot of difficulties. First of all by climate change, rising sea tides," Ban said ahead of a welcoming ceremony on Sunday night.

"That's why I am here, to show my strong solidarity and unity with the people of Samoa and many other small island states."

Low-lying island nations, some of which are little more than one metre (three feet) above sea level, are regarded as some of the most vulnerable to rising seas blamed on man-made climate change.

Some small states in the Pacific such as Kiribati have already begun examining options for their people if climate change forces them from their homeland.

World Bank special envoy for climate change Rachel Kyte said island nations did not create the problem and did not have the resources to deal with it, so the rest of the world was obliged to help.

"We have a responsibility towards these nations because we've pumped enough poison into the atmosphere over the last decades to imperil the livelihoods of many of the people in many of the atolls and islands of these nations," she told the Australian Broadcasting Corporation.

"This is the place where we have to roll up our sleeves as the international community and work alongside islanders to strengthen their economies."

As well as climate change, the conference will examine the problem of non-communicable diseases in Pacific countries which account for 75-85 percent of deaths, the World Bank said.

Other issues on the agenda include ways to improve sustainable management of oceans and fisheries.