As pro-democracy protests grind on for a fourth month, Hong Kong has been left counting the cost, with the city’s tourist industry battered and businesses forced to lay off staff as they struggle to stay afloat.

A passenger train derailed during the morning rush hour in Hong Kong on Tuesday leaving eight people injured, authorities said.

Images from the scene showed three carriages had left the tracks and were zigzagged across the rails near Hung Hom station in Kowloon -- a busy interchange that provides services to mainland China.

Riot police fanned out across Hong Kong on Saturday and thwarted plans by pro-democracy protesters to target the airport, days after the city's leader made a surprise concession which was rejected by the movement as too little, too late.

Prominent Hong Kong democracy activists were arrested Friday in a dragnet that came as protesters planned to rally this weekend in defiance of a police ban.

Beijing on Tuesday voiced "strong dissatisfaction" with a joint statement issued by the G7 leaders, who backed Hong Kong's autonomy and called for calm after months of civil unrest.

Hong Kong police on Monday said they were forced to fire water cannon and a warning shot to fend off "extremely violent" demonstrators, as months of pro-democracy protests veer deeper into violence.

Thousands of schoolteachers in Hong Kong marched to the official residence of the city's leader on Saturday as another weekend of protests got underway in the Chinese territory.

An overflow crowd rallied at a nearby public square before setting off on streets that had been closed to traffic, carrying signs that read "Protect the next generation" and umbrellas to ward off intermittent downpours.

Pro-democracy protesters retreated from Hong Kong's airport on Wednesday following two days of hugely disruptive rallies that turned violent and plunged the global financial hub further into turmoil.

China on Wednesday slammed pro-democracy protesters at Hong Kong airport for what it described as "terrorist-like" acts, after two men were beaten by demonstrators.

Hong Kong's leader warned pro-democracy protesters Tuesday against heading down "a path of no return", but they responded with a fresh rally at the city's airport a day after demonstrators triggered an unprecedented shutdown. 

The new gathering came as Beijing sent more ominous signals that the 10 weeks of unrest must end, with state-run media showing videos of security forces gathering across the border.