Hong Kong was bracing for potential violence on Friday after student groups warned of an escalation in protests over the government’s refusal to meet an ultimatum on the controversial extradition law.

Protesters, who have clogged the centre of the global financial hub with mass demonstrations in recent weeks, had demanded the resignation of Hong Kong leader Carrie Lam, the retraction of the bill, and police accountability over the firing of rubber bullets and tear gas on a rally last week.

The authorities said the government office buildings would be closed on Friday “due to security considerations” ahead of a fresh protest expected to start at 7am.

The controversial bill, which would allow some suspects to face trial in China, has this month prompted the largest demonstrations since Hong Kong’s handover to Beijing in 1997.

A record-breaking rally on Sunday, which organisers claim topped two million people, was carried out peacefully. But the city is still reeling from violent clashes between riot police and protesters on July 12.

On Thursday evening, plans for the latest wave of protests were still unclear in a movement that remains leaderless and largely driven by group brainstorming on social media forums.

Protesters discussed picnics, blocking toll roads and laying siege to the government and police headquarters.