Singapore police say they have killed a man and detained two others near a hotel hosting a top-level international security conference.
Defence ministers and leaders from the Asia-Pacific region were at the summit, known as The Shangri-La Dialogue.
Police say they opened fire after a car rammed through police barricades.
The summit ended with China defending its controversial policy of land reclamation in the disputed waters of the South China Sea.
Police say Sunday's shooting is under investigation, but that it appeared to be an isolated incident unrelated to the conference.
Extra security had been in place due to the conference, which was attended by senior defence leaders including US Secretary of Defence Ashton Carter, who spoke at the summit on Saturday.
On Sunday China rebuffed some of Mr Carter's strong criticism on China's land reclamation projects in the South China Sea, which he had said were "out of step" with international rules.
Shangri-La Dialogue: Big powers jostle
- Top officials from Singapore, the UK and EU repeat US calls for China and the Association of Southeast Asian Nations (Asean) to adopt a code of conduct in the disputed waters
- The US and Australia say they will continue to patrol what they consider to be international navigation zones in the South China Sea in spite of Chinese protests at "provocative moves"
- China says it will base a decision to create an Air Defence Identification Zone (ADIZ) - which requires overflying aircraft to identify themselves - in disputed waters on its assessment of the security situation.
The US says that through reclamation China has increased its acreage in the Spratly island group - also wholly or partly claimed by Taiwan, the Philippines, Vietnam, Malaysia and Brunei - by 400 times.
The Deputy Chief of the General Staff of the Chinese armed forces, Admiral Sun Jianguo, said that China's rights and interests there were "indisputable" but that it was exercising them "with enormous restraint".
He said China's island-building was about helping the region, by improving facilities for weather stations, scientific research, and search-and-rescue among other things.
Despite facing spirited questioning, he gave little ground, reports the BBC's world affairs correspondent Jonathan Marcus - and overall little progress was made at the meeting.
The incident near the hotel on Sunday began when a car was stopped at a vehicle checkpoint, but then accelerated after the passengers were asked to open the car boot.
Officers opened fire because the car "was endangering the lives of officers", the police statement said.
No weapons were found on the three men, but illegal drugs "and an item believed to be a drug-taking utensil" were found on one of those detained, police said.
The hotel and surrounding roads were briefly placed on lockdown.