Secretary of State Antony Blinken arrived in Australia Wednesday to meet Asia-Pacific allies concerned by China's rise and signal United States commitment to the region despite Washington's recent focus on Ukraine.

Blinken will join two days of meetings of the Quad grouping, aiming to strengthen the partnership with India, Australia and Japan as a bulwark against Beijing's growing economic and military might.

The top US diplomat admitted the possibility of Russia invading Ukraine has been "front and centre" for the US government, even as he flew to Melbourne for the fourth Quad foreign minister meetings.

However, he insisted that Washington's "pivot" to the Asia-Pacific region in the face of China's challenge is still alive, despite the powerful diversions of crises in the Middle East and now Eastern Europe in recent years.

"The world is a big place. Our interests are global and you all know very well the focus that we put on the Asia-Pacific and the Indo-Pacific regions," he told reporters aboard his plane.

"We have a sustained focus on this, and that's why we're heading to Australia."

The US has sought to broaden the Quad from a maritime security partnership to other areas, like fighting the coronavirus pandemic.

"The message that the secretary will take with him on this trip is that our partnerships deliver," US Assistant Secretary of State for East Asian and Pacific Affairs Daniel Kritenbrink said ahead of the trip.

"The Quad is a key component of US foreign economic and security policy in the Indo-Pacific region," he said.

Launched in 2007, the Quadrilateral Security Dialogue, or Quad, has given a framework to what began as joint US-India-Japan naval exercises in the Indian Ocean, dubbed the Malabar Exercises.

The arrangement gained new momentum in 2020 when Australia rejoined and Chinese and Indian troops engaged in bloody clashes in a contested border region which gave traditionally non-aligned New Delhi a push toward more engagement with the Quad.

Marise Payne, Australia's minister for foreign affairs, said the Quad ministers will focus on vaccine distribution in the region, on cyber and critical technology, countering malicious disinformation, counterterrorism and climate change, in addition to security.

"As a network of liberal democracies we are committed to very practical cooperation and ensuring that all Indo-Pacific nations -- large and small -- are able to make their own strategic decisions and make those decisions free from coercion," she told Australia's ABC radio. 

Blinken embarked on the trip to Australia only hours after a Washington press conference with top EU officials sought to show a united front on the threat presented by the estimated 140,000 Russian troops now massed on Ukraine's border.

"This is not alarmism. This is simply the facts," Blinken said at Monday's press conference.