Passengers board a train to Belgrade at Novi Sad station in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

Passengers take a selfie at Novi Sad station in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

A train is to leave Belgrade station for Novi Sad, Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

Passengers are to board a train to Belgrade at Novi Sad station in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

A train is to leave Novi Sad station for Belgrade, Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

Passengers wait at Novi Sad station in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

A passenger asks a staff member for help at Belgrade station in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

Passengers are to board a train to Belgrade at Novi Sad station in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

Passengers are to board a train to Novi Sad at the Belgrade station in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

Passengers chat on a train from Belgrade to Novi Sad in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

A passenger waits at Novi Sad station in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

Passengers board a train to Belgrade at Novi Sad station in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

A train is to leave Belgrade station for Novi Sad, Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)

Kids pose for a photo on a train from Belgrade to Novi Sad in Serbia, May 6, 2023. The 80-kilometer-long, Chinese-built Belgrade-Novi Sad high-speed railway has been carrying passengers at speeds of up to 200 kilometers per hour since March 2022. (Xinhua/Ren Pengfei)