SYDNEY, Jan 31 (Reuters) - Pacific Islands nations that want to connect to U.S.-funded undersea cables will need to secure their digital ecosystems to guard against data risks from China, a senior U.S. State Department official said.

The United States pledged last year to jointly fund two undersea cables, to be built by Google, connecting the U.S. territory of Guam with hubs in Fiji and French Polynesia, and further branching out across remote Pacific Islands.

The proposed intra-Pacific cable project has offered to branch out to Papua New Guinea, Samoa, Tuvalu, Fiji, Nauru, Marshall Islands, Kiribati, Cook Islands, Wallis and Futuna and the Federated States of Micronesia.

The U.S. Department of State’s ambassador at large for cyberspace and digital policy, Nathaniel Fick, visited Fiji this week as Washington prioritises which islands will have the opportunity to plug in.

The digital ecosystems in countries connecting to the cables need to be secured "from end to end", which excluded what he called "untrusted" Chinese-built datacentres or phone towers, he told reporters in Sydney on Wednesday.

"Investing a lot of money in these nodes is going to require these states to behave in some ways that mitigate the risk, to the greatest possible extent," he said.

"It's going to be in their interests to do that if they want to be trusted nodes for the long haul and attract continued investment."

China and the U.S. are jostling for influence in the Pacific Islands with competing offers for infrastructure. The Solomon Islands, which struck a security pact with Beijing, is rolling out a Chinese-funded mobile network built by Chinese telecommunications company Huawei.

Australian telecommunications company Telstra, a partner in the new U.S.-backed project, said in a statement this month the cables will "dramatically improve the diversity of paths between Guam to Australia via Fiji and other Pacific islands, and between the US mainland and Australia".

Guam is home to U.S. military facilities that would be key to responding to any conflict in the Asia-Pacific region, and Microsoft warned last year it had been targeted by a Chinese hacker group, Volt Typhoon, seeking to disrupt critical communications infrastructure between the U.S. and Asia in any future crisis. China said the hacking allegations were disinformation.

(Reporting by Kirsty Needham; Editing by Edwina Gibbs)