Pro-democracy protesters on Wednesday stepped up a “blossom everywhere” campaign of road blocks and vandalism across Hong Kong that has crippled the international financial hub this week and ignited some of the worst violence in five months of unrest.

The new phase in the crisis, which has forced schools and shopping malls to close as well as the shutdown of large chunks of the vital train network, has prompted police to warn the city is on the verge of “total collapse” and a “breakdown”.

China, facing the biggest challenge to its rule of the territory since it was handed back by the British in 1997, has insisted it will not buckle to the pressure and warned of even tougher security measures.

As they have since the start of the week, protesters on Wednesday choked roads and blocked traffic with anything they could lay their hands on including bricks, bicycles, couches and other materials.

Key arterials routes were targeted in morning and after-work peak hours.

Various lines on the subway — used daily by more than half of the city’s 7.5 million people — were also suspended, forcing many workers to stay at home.

In the Central business district, hundreds of people left their offices at lunchtime to join the more hardcore protesters setting up barricades outside luxury-item shops and headquarters of big financial firms.

Masked protesters dressed in their signature black were also locked in a series of tense standoffs at university campuses, following intense clashes on Tuesday night that saw police fire tear gas and rubber bullets.

Highlighting the growing security fears, mainland Chinese students began fleeing Hong Kong on buses and boats back across the border, according to police and universities, although it was not immediately clear how many had left.

The chaos was part of the largely leaderless protest movement’s new strategy branded “blossom everywhere”, in which small groups target as many parts of the city as possible to cause maximum disruption and stretch police resources.