Macau has cracked down on democracy activists who launched an online political referendum just months after campaigners in neighbouring Hong Kong held a poll pushing for genuine universal suffrage.

Macau police on Sunday detained five activists involved with the poll, which came ahead of the election for chief executive of the former Portuguese territory. Jason Chao, head of the Open Macau Society, which helped organise the poll, said he and four other activists were released later on Sunday. Macau authorities say the group violated a privacy law by collecting voters’ personal information.

Macau reverted to Chinese control in 1999 and became a special administrative region with the same status as Hong Kong. Chinese punters have spurred rapid economic growth in the territory, which relies heavily on its casino industry. But the rise in wealth, which has seen Macau jump past Switzerland in terms of per capita income, has sparked increased inequality and discontent among residents.