The United States has officially recognised the Pacific nations of Cook Islands and Niue, President Joe Biden announced, as he hosted regional leaders in a bid to wrest influence from China.

The announcement came at the start of a summit with the 18-member Pacific Islands Forum, where US officials said the president was confirming a more assertive American stance in the region.

Mr Biden said in statements that Washington recognised the Cook Islands and Niue as "sovereign and independent" states and would establish diplomatic relations with both.

The move would help maintain a "free and open Indo-Pacific region," he added.

President Biden said that the deals to recognise the two nations would also help curb illegal fishing, deal with climate change in a vulnerable region and boost economic growth.

The Cook Islands and Niue together have fewer than 20,000 inhabitants but constitute a sprawling economic zone in the South Pacific.

Both are self-governing nations in "free association" with New Zealand, meaning that their foreign and defence policies are in varying degrees linked to Wellington.

After decades of being treated as a relative backwater, the South Pacific has become an important arena for competition between the US and an increasingly assertive China.

China has ramped up its economic, political and military footprint in the strategic ocean region.

A lagoon in Rarotonga, the largest of the Cook Islands

There is "no question that there is some role that the PRC has played in all this," a senior White House official said, referring to China by the abbreviation of its formal name.

China's "assertiveness and influence, including in this region, has been a factor that requires us to sustain our strategic focus."

The forum brings together states and territories scattered across the Pacific Ocean, from Australia to sparsely populated micro-states and archipelagos.

But China's influence will be felt through the absence of the prime minister of the Solomon Islands, now closely aligned with Beijing.

Manasseh Sogavare, who was in New York last week to attend the United Nations General Assembly, did not extend his stay in the United States.

"We're disappointed that he's chosen not to come to this very special summit," another White House official said.

Mr Biden had been due to follow up last year's inaugural summit with a meeting of Pacific leaders this May, in Papua New Guinea.

However, he cut short an Asia trip and returned stateside to address a debt-ceiling crisis.

For the Washington summit, the White House prepared a full programme, beginning with an American football match yesterday.

The leaders travelled by train to Baltimore, where they were guests of honor at an NFL game between the city's Ravens and the Indianapolis Colts.

Today's agenda features meetings and a lunch with President Biden.

Tomorrow, the leaders will meet with top officials on climate and the economy, and spend time with US politicians.