Pro-democracy supporters show the thumbs-up signs during a kickoff ceremony for Friday’s official referendum on democracy in Hong Kong. Pic: AP.

HONG KONG (AP) — Tens of thousands of Hong Kongers have voted in an unofficial referendum on democratic reform that has alarmed Beijing and sets the stage for possible mass protests to shut down the Chinese capitalist enclave’s financial district.

Tensions are boiling over in Hong Kong, which came back under Chinese control in 1997, over how to choose the city’s next leader.

Organizers of the Occupy Central with Love and Peace movement say nearly 100,000 people have cast ballots online on proposals for electoral reform.

Beijing has pledged to allow Hong Kongers to elect the chief executive starting in 2017. Current leader Leung Chun-ying was picked by an elite pro-Beijing committee.

The three options on Friday’s ballot all call for the public to nominate candidates, which Beijing has rejected.