After arrival, Ri held bilateral talks with Chinese Foreign Minister Wang Yi during the ASEAN Regional Forum on Friday, News 1 reported.
The North Korean representative was also scheduled to meet with counterparts from Vietnam, Indonesia, India and Thailand, during the security dialogue, according to the report.
The China-North Korea foreign minister summit began at 2:40 p.m. on Friday at the Singapore Expo Convention Center.
The meeting began when Ri moved to a room where Wang had already arrived.
The North Koreans flew to Singapore on Air China, after transferring at the main airport in Beijing, according to News 1.
The two top diplomats are likely meeting for the first time since May 2, when Wang visited Pyongyang.
Neither side disclosed details of the planned talks, but it is likely they may have discussed China's potential involvement in declaring an end to the 1950-53 Korean War.
The South Korean government had previously raised the possibility of China's participation in a potential declaration, according to the report.
North Korea is participating in more bilateral talks with ASEAN member states than in 2017, when ASEAN states refused to hold bilateral meetings with countries other than China and Russia.
China has been extending diplomatic efforts toward both Koreas, as it tries to maintain some level of influence on key decisions on the peninsula.
NHK reported this week a top Chinese Communist Party official secretly visited South Korea mid-July.