US and Chinese warships have rushed to help Indonesia search for a crashed AirAsia plane, but analysts say more than altruistic motivations are at play with world powers jostling for influence.

On the surface, the sight of naval vessels from the world's strongest nations sailing close to each other in the Java Sea, with Russian military planes flying above, shows their willingness to unite in a time of disaster.

But those nations are also cleverly using the disaster to project their militaries as a force for good in Asia, observers say.

The AirAsia flight from Indonesia to Singapore crashed during stormy weather on December 28, claiming the lives of all 162 people on board.

With rough seas hampering the search for the wreckage and the bodies, Indonesia has gratefully accepted the help of military assets from many foreign nations including the United States, China and Russia.

"I don't think there's any question that this is also about building soft power," said John Blaxland, a senior fellow at Australian National University's Strategic and Defence Studies Centre.

"They are very conscious of the very positive spin-offs of constructive engagement in these kinds of scenarios. There are very significant and enduring benefits, Blaxland said.

- Soft foil for hard power -

For the United States, the crash offered a timely example to the region of the advantages of President Barack Obama's drive to increase US military assets in Asia.

The USS Fort Worth, one of two warships it deployed to the Java Sea, came from Singapore where it had just begun a 16-month "rotational deployment".

Such deployments are a key plank of the US efforts to beef up its military muscle in the Asia-Pacific, a strategy that has riled China.

"It shows they are prepared to contribute to humanitarian assistance. It's part of the soft foil for hard power in the region," Blaxland said.

Gregory Poling, a Southeast Asia analyst at the Washington-based think tank Center for Strategic and International Studies, also said such operations won or cemented regional friendships for the United States.

Aside from AirAsia, Poling cited the lead role the US military played in the international response to Super Typhoon Haiyan, which claimed thousands of lives in the Philippines in 2013, and help in last year's search for Malaysia Airlines Flight MH370.

"In the last few years, it has become apparent around Southeast Asia that the greatest benefit of a continued US security presence in the region is its ability to rapidly respond to HADR (humanitarian assistance and disaster relief) and search and rescue needs, and assist with maritime security," Poling told AFP.

- China learns from mistakes -

China, meanwhile, is starting to play a bigger role in regional disaster response efforts in a strategy widely perceived as trying to counter the United States and allay fears over the dramatic expansion of its military.

For the AirAsia crisis, China quickly deployed a Navy rescue vessel with divers on board, as well as experts in finding black box data recorders.

Blaxland said China's fast action and offer of more support showed it had learnt from the mistakes of Haiyan, when it only offered significant help after its meagre initial response was heavily criticised.

Beijing's foot-dragging was widely interpreted as due to its bitter row with the Philippines over competing claims to part of the South China Sea.

"The blowback across Southeast Asia over their tardiness reverberated in Beijing. It really hit home that they were being seen as more than unhelpful," Blaxland said.

"As a consequence, Beijing is much more attuned to the importance (of helping)."

Russian President Vladimir Putin also sent two military aircraft and divers to help in the search for the AirAsia wreckage.

The support has drawn attention after Russia did not help in the search for MH370, and with Putin enduring heavy criticism for his nation's alleged role in the shooting down of another Malaysia Airline plane, flight MH17, travelling over Ukraine in July last year.

"Russia is among them (AirAsia searchers) for obvious MH17 reasons -- taking care to be seen as a 'good player' after the shoot down," said Bridget Welsh, a political analyst and senior researcher at National Taiwan University.