Chinese censors and opponents of the protests sweeping Hong Kong are engaging in a cat-and-mouse game with demonstrators and commentators in a bid to stop news of the unrest spreading online and, in particular, reaching the mainland.

Tens of thousands of pro-democracy protesters have braved police tear gas to make their views known.

Spreading the word over Western and Chinese social networks is a lot safer, but it is becoming increasingly difficult as mobile phone networks are disrupted and concerns about possible surveillance grow.