The 32-nation alliance has used the pomp-filled set piece in the US capital to showcase its resolve against Russia and backing for Kyiv.

Their gathering has been overshadowed by political uncertainty in the United States as President Joe Biden -- who will give a press conference Thursday -- fights for his own political survival.

Zelensky will join his NATO counterparts at a giant convention center in the heart of the US capital after getting promises of new weaponry to bolster the defense of the skies over Ukraine.

But he has called on Kyiv's backers, especially the United States, to go further -- including by giving his outgunned forces greater scope to strike inside Russia.

"Imagine how much we can achieve when all limitations are lifted," Zelensky said on the sidelines of the summit.

NATO's leaders on Wednesday once again demurred from issuing his war-torn country a clear invitation to join their alliance.

Zelensky unleashed a diplomatic firestorm at a summit in Lithuania last year by lambasting NATO's reluctance on membership.

In a bid to soften any disappointment this time around, NATO leaders called Ukraine's path to membership "irreversible."

They also pledged to provide Kyiv a minimum of 40 billion euros ($43 billion) in military support "within the next year."

- China 'enabling' Russia -

Ahead of the sit-down with Zelensky, NATO will switch its focus to the growing challenge from China as it welcomes the leaders of Australia, Japan, New Zealand and South Korea.

NATO leaders have expressed their "profound concern" about the deepening ties between Beijing and Moscow.

A declaration from the summit released Wednesday called China a "decisive enabler of Russia's war against Ukraine" through its supplies of dual-use goods such as microchips that can help Moscow's military.

China "cannot enable the largest war in Europe in recent history without this negatively impacting its interests and reputation," the leaders said.

Beijing has already angrily rejected the accusations from NATO and says the US-led alliance is seeking an excuse to expand its influence eastwards.

The United States has been pushing its European allies for years to pay closer attention to the threats posed by China.

The summit in Washington will be the third such gathering attended by leaders from the four Asia-Pacific partners.

Several initiatives including bolstering cooperation against cyberattacks and disinformation with the partner countries are expected to be announced.

But the Pacific leaders' presence is more about signaling NATO's greater interest in the region at a time of growing competition between Washington with Beijing.

Worried by the potential return of Donald Trump to the White House after November elections, European allies see increasing their focus on China as a way of keeping the United States engaged.

"I think the message sent from NATO, from this summit, is very strong and very clear, and we are clearly defining China's responsibility when it comes to enabling Russia's war," NATO's outgoing secretary general Jens Stoltenberg said.