Beijing and Washington have long been the dominant powers in Southeast Asia, home to some of the world's fastest-growing economies. But the region is increasingly seeking alternative alliances amid unease over China's rising influence and perceptions of an unpredictable White House.

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"Specific Southeast Asian states are now seeking to diversify their strategic partnerships, beyond a binary choice between Beijing and Washington," the Council on Foreign Relations, a U.S. think tank, said in a note this week.

A key element of those diversification efforts is working with India "as a more forceful counterweight to China and hedge against a declining United States," the note said.

Southeast Asian nations are also looking at Australia as another potential partner.

The Association of Southeast Asian Nations (ASEAN) and Canberra are holding a special summit between from March 16 to 18, a sign that the 10-nation bloc is exploring various hedging strategies against Beijing, said Geoff Raby, former Australian ambassador to China.

Trade deals such as the newly-inked Comprehensive and Progressive Agreement for Trans Pacific Partnership as well as intelligence sharing efforts on terrorism are also indicative of Southeast Asian leaders seeking greater regional cooperation.

US 'increasingly unreliable'

Certain countries, such as Cambodia and Thailand, haven't signaled opposition to Beijing's growing clout in the area, which is reflected by an influx of Chinese-funded infrastructure projects under the Belt and Road Initiative and man-made Chinese islands in the South China Sea.

But others, including Vietnam, have publicly come out against China's behavior in the region.

Previously, those nations could turn to Washington for leadership, but President Donald Trump's controversial measures — from tariffs on foreign aluminum and steel imports to firing Secretary of State Rex Tillerson — has unnerved America's Asian allies, according to strategists.

"The manner in which Donald Trump handled Tillerson's dismissal, combined with his snap decision to meet Kim Jong Un and other recent actions, reinforce the perception of the U.S. in Asia that the U.S. is increasingly unreliable," said Philip Yun, executive director of Ploughshares Fund, an anti-nuclear weapons group.

People in the region are paying attention to the fact that Japanese Prime Minister Shinzo Abe, "who had touted his close relationship with Trump, was blinded-side by Trump's agreement to a U.S.-North Korea summit," Yun said.

Also telling are recent comments from Singaporean Prime Minister Lee Hsien Loong, Yun said. This week, Lee said ASEAN must adjust to a new power balance in Asia, suggesting the bloc look more to China and India.

The U.S. is still widely expected to continue strong defense ties with Southeast Asian countries on matters such as freedom of navigation in the South China Sea.

India's rise in Southeast Asia

Widespread apprehension over China's ambitions has helped Prime Minister Narendra Modi enhance political and economic ties with Southeast Asian economies under a policy known as "Act East."

Hanoi, for example, is partnering with New Delhi on South China Sea issues. In a meeting earlier this month, Modi and Vietnamese President Tran Dai Quang committed to more defense equipment deals and joint exploration in the international waterway, prompting criticism from Beijing.

"The two sides may, in the future, want to be close partners to some other future regional alternative, or at least, partial alternative, to Belt and Road," according to the Council on Foreign Relations.

Vietnam is also strengthening relations with other regional powers that are skeptical of or outright hostile to China, the organization said.

And in January, India invited all 10 ASEAN leaders as chief guests to its annual Republic Day celebrations — a historic first. The same month, New Delhi also invited those politicians to a summit aimed at promoting maritime security.

Every ASEAN leader wants New Delhi to play a more assertive role in the Indo-Pacific region, Preeti Saran, secretary at India's Ministry of External Affairs, was quoted as claiming at the time.

India is also a major player in a newly resurrected informal defense alliance known as "the Quad," which is aimed at offsetting Chinese maritime expansion.

While Vietnam, Singapore and Indonesia are gradually embracing the concept of a more assertive Indian role in Southeast Asia, others like the Philippines and Malaysia remain silent on the matter, Manoj Joshi, distinguished fellow at Indian think tank Observer Research Foundation, said in a February report.

Australia too

Like India, Australia isn't a member of ASEAN, but Canberra has long been a major player in Asia-Pacific affairs due in part to proximity.

This weekend's summit between ASEAN leaders and Australian Prime Minister Malcolm Turnbull is "unprecedented," according to Raby: "Five, certainly 10 years ago, this would have never happened, ASEAN leaders would not have come to Australia, they would not have embraced Australia in this way."

Uncertainty over China and the U.S. is pushing Southeast Asia to Down Under, Raby said.

China's "aggressive and assertive foreign policy in Southeast Asia" is motivating regional governments to seek "a balance on Beijing's behavior," he said.

Moreover, ASEAN is worried about "how engaged the U.S. will be in East Asia" amid uncertainty over Trump's policies, Raby continued.