With China offering no concessions, protesters switched tactics and launched a campaign to cause as much disruption as possible. (AFP)

Hong Kong pro-democracy protesters defied a warning by China’s President Xi Jinping and took to the streets again Friday, as the political turmoil seeped out to London, where a territorial minister was confronted by masked demonstrators.

Protests have swept Hong Kong since June as many in the city of 7.5 million people have vented fury at eroding freedoms under Chinese rule.

Violence has escalated, and tensions have spread overseas, sparking friction between China and Britain, which governed Hong Kong until 1997.

Hong Kong Justice Secretary Teresa Cheng fell in London Thursday after being surrounded by pro-democracy protesters, in the most physical confrontation involving a minister since the unrest began.

Cheng walked away without signs of injury, but Beijing slammed the incident as an “appalling attack” and accused Britain of fuelling the protest movement. Police in London said they were investigating.

Former colonial power Britain has urged Beijing and Hong Kong to seek a political solution to the crisis and has condemned escalating violence on both sides.

In Beijing, Chinese foreign ministry spokesman Geng Shuang said if Britain “continues to add fuel to the fire… then it will bring calamity on itself.”

Thousands of mainly office workers took to the streets of the Chinese territory, many chanting “Stand with Hong Kong” and raising an open hand with five fingers splayed — a reference to the five protester demands which include the right to freely elect Hong Kong’s leaders and an independent inquiry into alleged police brutality.

“Every person in Hong Kong has a role to play,” James, a 33-year-old banking employee told AFP, adding “sacrifice” was necessary to keep the wind behind the protest movement.

Protesters also occupied university campuses, while the city endured another day of transport chaos with service suspensions on the vandalised train network and roads blocked by barricades.

Two German students, aged 22 and 23, were swept up in the protests and arrested on Thursday for “unlawful assembly,” police said early Saturday.

According to Germany’s Bild newspaper, the two are exchange students at Hong Kong’s Lingnan University.

The German foreign ministry said it was “providing consular care … and is in contact with a lawyer and local authorities.”

Major universities in the Netherlands are advising the nearly 300 Dutch students in Hong Kong to quickly return home for security reasons.

“The clashes are getting close to campuses,”

University of Amsterdam spokeswoman Annelies van Dijk told AFP. “Students no longer feel safe there and their families are worried.”