Tony Leung and Tong Dawei in Lost in White. [Photo/China Daily]

Leung, who has played many cop roles in Hong Kong films, notes that it's his first time to play a mainland policeman.

"The filming environment is more challenging," says Leung.

Most of the footage was shot during the winter in Yichun, Northeast China's Heilongjiang province, where the average temperature was around minus 40 C.

To make one take featuring a drop into the river more realistic, Leung insisted on soaking himself from head to toe before jumping into the chilly water.

"He is very professional and hardworking. Sometimes it really surprised me as Leung has already established himself as a top idol in the industry," says Tong.