An international relations expert says this year's East Asia Summit could be more significant than previous ones.

Jacinda Ardern is set arrive in Bangkok to discuss trade and international instability, just days after APEC was cancelled due to ongoing unrest in host nation Chile.

Stephen Jacobi from the NZ International Business Forum says there could be a lot at stake, including a multilateral trade deal bigger than the controversial CPTPP.

"The Regional Comprehensive Economic Partnership - it's the trade deal that no one's heard of - it's a big deal. It's bigger than TPP, the Trans-Pacific Partnership." 

The Regional Comprehensive Economic Partnership covers more than a quarter of global trade and, with the inclusion of China and India, half the world's population. India has been the sticking point so far, fearing a flood of cheap Chinese imports.

Jacobi says the summit will be a major test for the Prime Minister. 

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"It's not all cocktail parties and dressing up in funny shirts - it's more than that. It's a really big deal. This year, because APEC is not taking place, it's going to be even more important."

He says New Zealand could play a big role in calming trade wars too. 

"Times are tough internationally at the moment. New Zealand isn't immune from these big global movements. As a small nation with an independent foreign policy, sometimes we can help build consensus... I'm sure the Prime Minister will be trying to do that."

Malaysian Prime Minister Mahathir Mohamad said the region's nations must stick together to fight US President Donald Trump's trade war.

"We don't want to go into a trade war. But sometimes when they're un-nice to us, we have to be un-nice to them," he said ahead of the summit, suggesting things will improve once Trump is out of office.

"If the person is not there, maybe there will be a change."

The US is sending a delegation, but it will be smaller than in previous years.

"This signals that the US is a lesser player in our area," Kantathi Suphamongkhon, former Thai Foreign Minister told Reuters.

Other issues expected to be up for discussion include maritime disputes between China and its neighbours and the Rohingya refugees situation.