When Japan invaded China in 1937, Lee, who was known for his association with China's Kuomintang Party, headed the Selangor China Relief Fund in support of China. He was later made Chief of the Passive Defence Forces of Kuala Lumpur in 1941. Due to his anti-Japanese war efforts, Lee was forced to flee with his family to Mumbai via Chongqing when the war reached Malaya that same year and the Japanese put out a bounty on him.