The following year, when the Japanese invaded Java and interred all the European physicians in 1943, Thung opened a private clinic, "San Te Ie Juen" to provide medical service to the upper classes. She continued her own private practice and did volunteer work at a local hospital for the duration of World War II. In 1945, when nationalists declared Indonesian independence, Batavia was renamed Jakarta. From 1945 to 1951, Thung was employed by the Ministry of Education to monitor the health of all of the school children in the city. She measured the height and weight of students for the Institute for Public Nutrition and monitored the milk supplements and food provided by the schools to ensure that they were provided in accordance with UNESCO standards.