Australia and Tuvalu have declared there are only a "narrow set of circumstances" where the federal government might trigger a contentious part of the Falepili Union which allows Canberra to veto security arrangements struck by the Pacific Island nation.

Both nations have released a new explanatory memorandum on the landmark migration and security pact during a bipartisan trip to the country by Foreign Minister Penny Wong and her Coalition counterpart Simon Birmingham.

Senator Wong also announced $110 million in development initiatives for Tuvalu, including $50 million for Tuvalu's first undersea telecommunications cable, an additional $19 million for coastal adaptation and $10 million in direct budget support.

The foreign minister told a large audience in the capital Funafuti that Australia's commitments under the Falepili Union were an "expression of our sincerity, an embodiment of our commitment to this partnership".

"The Falepili Union is about our collective sovereignty, safeguarding our future and supporting the people of Tuvalu to stay and thrive in your homeland," she said.

"These steps we are taking together – they represent steps Australia has taken with no other country."

Under the agreement, Australia has promised to bolster Tuvalu's coastal defences and open a resettlement pathway to 280 citizens every year, recognising that the low-lying nation faces an increasingly uncertain future in the face of climate change and rising seas.

Australia has also extended a security guarantee to Tuvalu, promising to come it its aid if it faces military aggression, a humanitarian disaster or a global pandemic.

But the agreement also says Australia would have to "mutually agree" to any security arrangements that Tuvalu wants to strike with other countries.

That has drawn criticism from some politicians in Tuvalu, with former prime minister and opposition MP Enele Sopoaga accusing Australia of trashing the Pacific nation's sovereignty.

The explanatory memorandum released on Thursday by both countries stresses there is only a "narrow set of circumstances for third-party cooperation" which might cause concern and trigger that clause.

It also stresses that Tuvalu would not have to consult with Australia over any security arrangements it strikes with other Pacific Island nations.

Analysts say the most likely scenario that might trigger consultation or a potential veto would be if a future government in Tuvalu decided to recognise China and then tried to strike a security or policing agreement with Beijing.

At the moment Tuvalu maintains ties with Taiwan rather than China, with the Prime Minister Feleti Teo committing to maintain that relationship – but there has been persistent speculation that the country might make the switch to Beijing in the future.

Both countries have made it clear that nothing in the agreement would prevent Tuvalu from switching diplomatic recognition if it chooses to do so.

Mr Teo was one of the eminent Tuvalu citizens who helped advise the previous government on the agreement and has spruiked the benefits of the pact for his country, saying it will help his country build up coastal defences while providing those who wish to leave with a "dignified" path to life in Australia.

The explanatory memorandum says that those who resettle in Australia will enjoy additional benefits and rights, being granted "indefinite permanent residency, with freedom for unlimited travel to and from Australia".

It also says the initial annual allocation of up to 280 visas "could be mutually adjusted each program year".

Mr Teo has also acknowledged that people in the Pacific nation weren't sufficiently consulted ahead of the agreement first being signed by Prime Minister Anthony Albanese and his predecessor Kausea Natano, and has launched a new education campaign on the pact.

The two countries are both planning to ratify the pact this year, but the explanatory memorandum says Australia will need to help Tuvalu modernise its border and immigration controls before the new migration pathway can be opened.

It says the new pathway should become active "around nine months after entry into force of the treaty".