The Touch Base Policy in British Hong Kong
Wikipedia:
the influx of immigrants continued, especially during the Cultural Revolution. In response the Hong Kong Government adopted the Touch Base Policy in November 1974, which allowed immigrants from Mainland China who reached the urban areas (reaching south of Boundary Street) and met their relatives to register for a Hong Kong Identity Card. Those who were intercepted in the Closed Area would be repatriated back to the Mainland immediately.
The Touch Base Policy failed to halt the influx of immigrants, and was abolished by the Hong Kong Government on 24 October 1980.