Participants run from the start during the "Happy Birthday L.A. 5K 2018" in Los Angeles, the United States, Sept. 2, 2018. Thousands of runners participated in the event to commemorate the Los Angeles City's 237th birthday. (Xinhua/Zhao Hanrong)

A participant wearing a mask runs during the "Happy Birthday L.A. 5K 2018" in Los Angeles, the United States, Sept. 2, 2018. Thousands of runners participated in the event to commemorate the Los Angeles City's 237th birthday. (Xinhua/Zhao Hanrong)

A group of participants pose for photos before the "Happy Birthday L.A. 5K 2018" in Los Angeles, the United States, Sept. 2, 2018. Thousands of runners participated in the event to commemorate the Los Angeles City's 237th birthday. (Xinhua/Zhao Hanrong)

People cheer on runners during the "Happy Birthday L.A. 5K 2018" in Los Angeles, the United States, Sept. 2, 2018. Thousands of runners participated in the event to commemorate the Los Angeles City's 237th birthday. (Xinhua/Zhao Hanrong)

Participants run during the "Happy Birthday L.A. 5K 2018" in Los Angeles, the United States, Sept. 2, 2018. Thousands of runners participated in the event to commemorate the Los Angeles City's 237th birthday. (Xinhua/Zhao Hanrong)

A participant runs with his dog during the "Happy Birthday L.A. 5K 2018" in Los Angeles, the United States, Sept. 2, 2018. Thousands of runners participated in the event to commemorate the Los Angeles City's 237th birthday. (Xinhua/Zhao Hanrong)

Participants run during the "Happy Birthday L.A. 5K 2018" in Los Angeles, the United States, Sept. 2, 2018. Thousands of runners participated in the event to commemorate the Los Angeles City's 237th birthday. (Xinhua/Zhao Hanrong)