Three activist groups in Chinese-ruled Macau, the world's biggest gambling hub, are planning an informal referendum on democracy, an organizer said Tuesday, following the footsteps of neighboring Hong Kong, whose ballot China branded illegal.

Macau, a special administrative region of China like Hong Kong, is widely expected to re-elect its current leader, Fernando Chui, in a vote on Aug. 31.

But it is an official body of 400 that elects the leader, similar to Hong Kong, where a small committee of largely pro-Beijing loyalists chooses who gets on the ballot, effectively rendering the ability to vote meaningless.