Since the 1997 handover of Hong Kong to China, the semi-autonomous city has operated under a "one country, two systems" formula, allowing a limited democracy. In August, the Chinese government announced plans to vet candidates in Hong Kong's 2017 elections, virtually assuring only pro-Beijing politicians would be on the ballots. Student groups and pro-democracy supporters have taken to the streets in recent days to protest the limitations and to demand universal suffrage. Tens of thousands of demonstrators have occupied Hong Kong's Central District, bringing parts of the city to a standstill. The protests are one of the largest political challenges to Beijing since the 1989 Tiananmen Square crackdown. Chinese officials have scolded protesters and warned against any foreign interference.