There was no immediate explanation from the government as to why more bilateral meetings could not be arranged between Khan and other world leaders
Chinese Commerce Minister Zhong Shan had invited India to participate in the event, an Indian Embassy press release said.
China and Japan have had uneasy ties since World War II over the invasion of Japanese Army and its alleged large-scale atrocities.
They also "explored various confidence building measures with a view to further enhance mutual trust and understanding," it said.
According to sources, President Xi had paid personal attention to small details.
PM Modi, Chinese President Xi Jinping agree to issue strategic guidance to their militaries to strengthen communications: Foreign Secretary Vijay Gokhale
Gokhale said the two leaders underscored that it is important to maintain peace and tranquillity in all areas of the India-China border region.
Modi and Xi are due to conclude their unprecedented informal summit today, seen as an effort by India and China to rebuild trust and improve ties.
Swaraj's meeting with the Chinese President comes a day after the two countries announced a summit meeting between Xi and Prime Minister Modi at Wuhan this week.
China said Narendra Modi and Xi Jinping will discuss globalisation and the threat of rising protectionism at their informal summit at Wuhan this week.
Kim has agreed to meet with South Korean President Moon Jae-in in the Demilitarized Zone in late April, while Trump and the North Korean leader could meet by the end of May.
Chinese President Xi Jinping praises Communist Party of China rule, says multiparty democracy promotes nasty competition
The Chinese system is new, Xi said, because it unites all political parties and people without party affiliation toward a common goal.
Removal of two-term limit for President Xi Jinping important to uphold Communist Party's unity: China
The Communist Party of China's Central Committee has proposed to remove the two-term limit for the post of president and vice president through a constitutional amendment.
The Central Committee proposed removing the clause that the President and Vice-President 'shall serve no more than two consecutive terms' from the country's Constitution.
The US President praised Xi for his statement at the Asia-Pacific Economic Cooperation Summit on denuclearisation of the Korean Peninsula.
Xi's concept of "socialism with Chinese characteristics for a new era" was added to the party constitution at the close of a twice-a-decade major congress.