Australia's signing of a declaration calling climate change the "single greatest threat" to the Pacific region must be followed up with real action on emissions, environmental groups say.

Leaders capped off the 18-nation Pacific Islands Forum on Wednesday by signing the “Boe Declaration”, expanding on security themes to include the environment, cybercrime and transnational crime.

As was widely expected, the forum communique said climate change presented “the single greatest threat to the livelihood, security and well-being of Pacific people” and underscored the need for “immediate urgent action”.

Leaders also called on large emitters to fully implement national emissions mitigation targets and for the United States to return to the Paris Agreement on tackling climate change.

However Tuvalu’s prime minister Enele Sopoaga is reported to have later told media a country whose name started with ‘A’ – Australia being the only candidate – had raised concerns about some of the language around climate change during talks.

Comment has been requested from the Department of Foreign Affairs and Trade about whether Australia objected to parts of the declaration.

The focus on climate change recognises concerns that have been the key priority for Pacific leaders at the annual meeting.

New Zealand Prime Minister Jacinda Ardern called the Boe Declaration the most significant statement on the region’s security in a generation.

“Modern-day regional security challenges include climate change, cybercrime and transnational crime,” she said.

New Zealand’s foreign ministry, in a statement, said it had supported all climate change clauses in the declaration.

The Australian Conservation Foundation said the signing of the declaration was an important recognition of the issue by the new Morrison government but needed to be followed up with policy.

“This international commitment by our nation must be matched by domestic action,” ACF chief Kelly O’Shanassy said.

“Australia’s climate pollution is rising and we have observed another collapse of domestic policy to cut emissions from electricity generation.”

Australian opposition foreign affairs spokeswoman Penny Wong has echoed the sentiment.

“It is now essential Mr Morrison shows Pacific island states that Australia’s support for the declaration is more than just words by committing to genuine action on climate change to meet Australia’s Paris targets,” she said.

Ahead of the forum, Australian ministers tried to ease concerns among Pacific leaders about their seriousness on climate change, saying the government was still committed to reduction targets despite the recent collapse of planned emissions legislation.

“There’s no doubt the Pacific islands would have a dim view of Australia reducing its commitment to climate change measures – reducing our emissions footprint,” Defence Minister Christopher Pyne told Sky News.

“But we have no plans to do so.”