Singapore's Prime Minister hosts an ASEAN working dinner in Singapore, April 27, 2018. (Photo: AFP)

Singapore's Prime Minister Lee Hsien Loong said on Saturday a trade row between the United States and China was one of the most pressing concerns for Southeast Asian nations.

Lee flagged his concerns in remarks made as he opened a summit of the 10-member Association of Southeast Asian Nations (ASEAN), for many of which the United States and China are the top two trading partners.

"In particular, the recent trade tensions between the US and China are worrying concerns,” Lee said as ASEAN members gather for the organization's 32nd summit.

The Trump administration has threatened to impose tariffs on up to 150 billion US dollars of Chinese imports, and Beijing has vowed retaliation against American exports.

On Saturday Lee said the open and rules-based multilateral trading system, which has backed the growth of ASEAN member states, has come under pressure as the political mood in many countries has shifted against free trade.

Other agenda at the summit include the South China Sea issue. The bloc is working to negotiate a code of conduct with China to ease tensions in the disputed water.

Lee told his counterparts that it is better to spend time and discuss about the code of conduct constructively and try to keep the temperature down.

It is unclear how much substantive progress could be accomplished on the code of conduction but analysts say there is definite sign of progress on reaching a final code of conduct that the parties committed to 15 years ago.