Leaders from the 18-member bloc travelled to Tonga in August for an annual meeting dominated by the growing Pacific rivalry between China and the United States.

Months earlier, with meeting preparations in full swing, staff noticed a computer breach at the forum's headquarters in Fiji.

"New Zealand has been briefed on a cyber incident affecting the Pacific Islands Forum Secretariat systems," a spokesman for New Zealand's foreign minister said on Thursday.

"We remain concerned by the growing number of malicious cyber incidents in our region, targeting national entities and regional organizations," the spokesman added.

It was not clear who was behind the breach, or what information may have been targeted.

But it was considered serious enough at the time that a rapid response team of Australian specialists was sent to help at the forum's request.

"Responding to cyber threats and building resilience is a priority for Australia, both at home and in our region," said Australia's foreign affairs department. 

Forum secretary Baron Waqa, who has warned China and the United States to take their "fight" out of the Pacific, would address the incident on Friday, a spokeswoman said. 

The Pacific Islands Forum has captured increased global attention as China vies for regional influence against the United States and its allies. 

Its members include nations with close links to Washington, others who are warmly disposed to Beijing, and some who still maintain diplomatic ties to Taiwan. 

Solomon Islands, China's main partner in the South Pacific, has been lobbying for Taiwan to be stripped of its "development partner" status with the forum. 

The August meeting was notable for a joint declaration that appeared to reaffirm support for Taiwan's limited participation.

But this wording immediately raised the ire of Chinese diplomats, who piled pressure on Pacific leaders to amend the document. 

The forum reissued the declaration without the offending paragraph, which referenced the bloc's long-standing "relations with Taiwan". 

In a subsequent explanation, it said the references to Taiwan had been included by mistake.

Asked Thursday about reports in Australian media that Beijing was behind the hack on the Pacific Islands Forum, China's foreign ministry slammed it as "false information, fabricated for political purposes".

"Its aim is to sow discord between countries in the region and China," spokeswoman Mao Ning said.