Scott Morrison and Chinese Premier Li Keqiang were two of the world leaders at the ASEAN summit.

Leaders of 15 Asia-Pacific nations have agreed to terms on the world's largest trade deal, pressing ahead with the pact even though India refused to join.

Key points: The Regional Comprehensive Economic Partnership covers about 29pc of the global economy

The pact formalises trade rules across the 15 countries and gives Australia better access to those markets

India declined to join the pact, amid concerns it would undermine the nation's already-faltering economy

The Regional Comprehensive Economic Partnership (RCEP) was to be a deal with the 10 South-East Asian members of the ASEAN alliance, and Japan, China, South Korea, New Zealand, Australia and India.

But in battling domestic concerns the RCEP would undermine an already-faltering economy, Indian Prime Minister Narendra Modi held out on joining others at the East Asia Summit in agreeing to terms.

With India in the deal, the RCEP would have covered 32 per cent of the global economy, and half the world's population. Without India, it covers about 29 per cent of the global economy.

Australia already has individual trade agreements with ASEAN and a number of other countries in the deal, but this pact formalises trade rules across the 15 countries and gives better access to those markets beyond what the original deals allow.

"We have been through this sort of process with big trade agreements before in relation to the Trans-Pacific Partnership," Trade Minister Simon Birmingham said before the announcement.

"Of course, we had hoped and expected the United States to be part of that. The door in the TPP remains firmly open to the US.

"We want India to be a partner here as well but we have to make sure that progress is realised amongst the 15 nations who are there without India."

Mr Modi has faced domestic pressure to avoid the deal, amid fears it would undermine India's manufacturing industry.

His country already has a $60 billion trade deficit with China and there are concerns lowering tariffs, and allowing the flow of cheap Chinese products into India, would further increase that deficit.

India's farm sector is also concerned it could suffer under any deal that allows for greater imports of agricultural products.

The leaders signing up to the RCEP are leaving the door open to India to join the pact in the future, if the country is able to agree to terms.

It is now likely the RCEP will be formally signed sometime next year.

The Federal Government said Australian firms working in health care, education and professional services, such as law and accounting firms, would benefit under the new deal.

Prime Minister Scott Morrison met with his Indian counterpart earlier, and spoke of the strong ties between the two nations.

India is one country Australia does not have a separate trade deal with, and had hoped to secure some access to under RCEP.

Mr Morrison is due to visit India in the coming months.

US accuses China of 'conquest' in South China Sea

On the sidelines of this year's ASEAN summit, a US envoy accused China of "intimidation" in the South China Sea, and said smaller countries in the region should not give up their resources by way of Beijing's "conquest".

The comments join a long line of Washington's criticism of Beijing's activities in the disputed waterway — which it claims almost in its entirety — involving the militarisation of the sea's coral reefs in contravention of international law that has rejected some of China's claims.

"Beijing has used intimidation to try to stop ASEAN nations from exploiting the off-shore resources, blocking access to $US2.5 trillion ($3.63 trillion) dollars of oil and gas reserves alone," Robert O'Brien, White House National Security Adviser, said.

"We don't think they should be handled by intimidation or through maritime militias or by random ships or by surrounding islands … That's just not how things should be done in the 21st Century. That's conquest."

Disputes should be handled peacefully, he added.

This article includes interactive enhancements which are not supported on this platform. For the full interactive experience in this article, you will need a modern web browser with JavaScript enabled. Find out more about browser support at ABC News Online.

Vietnam, China, Malaysia have eyes on the prize

*



Rich in resources and traversed by a quarter of global shipping, the South China Sea is the stage for several territorial disputes that threaten to escalate tensions in the region.

At the heart of these disputes are a series of barren islands in two groups - the Spratly Islands, off the coast of the Philippines, and the Paracel Islands, off the coasts of Vietnam and China.

*



Both chains are essentially uninhabitable, but are claimed by no fewer than seven countries, eager to gain control of the vast oil and gas fields below them, as well as some of the region's best fishing grounds.

Indonesia, Malaysia and Brunei have made claims to part of the Spratlys based on the internationally recognised Exclusive Economic Zone (EEZ), which extends 200 nautical miles from a country's coastline.

*



Based on the EEZ, the Philippines has the strongest claim on the Spratlys and their resources, with its EEZ covering much of the area.

However the lure of resources, and prospect of exerting greater control over shipping in the region, means that greater powers are contesting the Philippines' claims.

*



China has made extensive sovereignty claims on both the Spratlys and the Paracels to the north, based largely on historic claims outlined in a map from the middle part of the 20th Century known as the 'Nine Dash Map'.

Taiwan also makes claims based on the same map, as it was created by the nationalist Kuomintang government, which fled to Taiwan after the communists seized power in China.

*



Vietnam also claims the Spratlys and the Paracels as sovereign territory, extending Vietnam's EEZ across much of the region and bringing it into direct conflict with China.

There have been deadly protests in Vietnam over China's decision to build an oil rig off the Paracels.

One Chinese worker in Vietnam was killed and a dozen injured in riots targeting Chinese and Taiwanese owned factories, prompting 3,000 Chinese nationals to flee the country.

*



EEZ can only be imposed based on boundaries of inhabitable land, and this has prompted all the countries making claims on the region to station personnel, and in some cases build military bases out of the water, to bolster their claim.

Building and protecting these structures has resulted in a series of stand-offs between countries in the region, each with the potential to escalate.

China has been leading the charge with these installations, and has deployed vessels to the region to protect their interests.

Chinese coast guard vessels have used a water cannon on Vietnamese vessels, as well as blockading an island where the Philippines has deployed military personnel.



This drew a rebuke from Chinese Vice Foreign Minister Le Yucheng, who said it was unacceptable for countries from outside the region to come "to make waves, escalate disputes and create tensions".

Mr Le emphasised progress on the code of conduct for the South China Sea which Beijing is discussing with ASEAN countries.

Mr O'Brien delivered an invitation from Mr Trump to the ASEAN leaders to a special summit at some point in the first quarter of 2020.

At this year's summit, US Commerce Secretary Wilbur Ross was the highest-ranking delegation official, prompting the 10-member ASEAN to downgrade its participation at the meeting to only leaders from Thailand, Vietnam and Laos.

China was represented at meetings in Bangkok by its premier, Le Keqiang.

Despite the South China Sea accusations, Mr O'Brien said Washington sought a "great relationship" with China and that the two sides were close to a "phase one" agreement to begin to roll back a 16-month trade war.

With additional reporting from Reuters