The US had the ability to provide deterrence and ensure a free and secure Indo-Pacific even before Australia becomes ready to deploy nuclear-powered submarines, she said.

Ms Kennedy, who would be the 27th US ambassador to hold the position, is expected face no opposition from Republican senators on her confirmation and be able to take up the Canberra posting later this month.

US senators grilled Caroline Kennedy overnight on Australia's collapsed relationship with China, concerns about the Solomons Islands' security talks with China, and the climate crisis disasters devastating Australian communities.

Former Republican nominee for president Mitt Romney told the hearing Ms Kennedy had important work to do in Canberra as Australia was a very important ally with "backbone" in standing up to China for behaving in a "malevolent and predatory way".

China was a real threat to US interests, he said, but appeared to have a successful strategy to expand their influence, both militarily and economically.

"I'm concerned that we as a nation and even members of the Quad [Australia, India, Japan and the US] have not settled on what our strategy is to deal with China," Senator Romney said.

Senator Bill Hagerty, also a Republican, wanted to know Ms Kennedy's views on the Chinese Communist Party's security bilateral talks with the government of the Solomon Islands. Government officials in Washington DC have been as concerned as the Australian government at the prospect of China obtaining a military presence on the islands.

Ms Kennedy said the reopening of the US embassy in the Solomon Islands "can't come soon enough".

The US had the ability to defend a free and secure Indo-Pacific she said, in partnership with Australia.

The AUKUS technology sharing pact which, allows Australia access to nuclear-powered submarines, as well as cooperation on AI, quantum, cyber and undersea technologies would provide "a lot of deterrence ... well before the submarines are in operation," she said.

"This is a vital region, and I think that we need to be more visible," Ms Kennedy told the hearing.

"But I think that [with] our long record in the region of support and assistance over many years, if we are able to build on that, we can make a difference."

Extreme climate disasters in Australia was another issue in which US senators took interest, with the chair of the foreign relations committee, Democratic senator Bob Menendez, noting the high cost of fires, floods and ocean acidification killing thousands of acres of the Great Barrier Reef.

"There are great lessons for the United States to learn to how to prepare for such extreme climate disasters, and how to get Australia to think about the climate responsibilities they have," Senator Menendez said.

Ms Kennedy agreed there was much to learn about these kinds of disasters and the transition to clean energy to reduce the impacts of climate change.

"The faster we can do that, if confirmed, I would be eager to work on that," she indicated.

The only surviving child of former president John F Kennedy, and having previously served as ambassador to Japan, Caroline Kennedy has broad support in American political life.

The two-hour confirmation hearing in the early hours of Friday, Australian time, also heard from White House nominees for Korea (Philip Goldberg), the Philippines (MaryKay Carlson) and Norway (Marc Nathanson).