In June 1948, an armed insurgency by communist groups in Malaya broke out, and the British imposed harsh measures to control left-wing groups in both Singapore and Malaya; the controversial Internal Security Act, which allowed indefinite detention without trial for persons suspected of being "threats to security", was enacted in Singapore at this time. Since the left-wing groups were the strongest critics of the colonial system, progress on self-government stalled for several years. The colonial government also tried to prevent contact between Singaporean Chinese and the People's Republic of China, which was proclaimed by the Communist Party of China in October 1949. Tan Kah Kee, a Singapore businessman and philanthropist, made a trip to China in 1949 and was denied re-entry into Singapore when he planned to return in 1950.