Activists prevented trains from leaving across the city. Some blocked doors while others sounded emergency alarms.
Crowds of passengers were left stuck on subway platforms and services were badly delayed for much of the morning.
Anti-government protests have rocked the city in recent weeks and are causing ongoing disruption.
The demonstrations began over a controversial bill that would have enabled extraditions to mainland China, but they have since morphed into a broader movement focused on democratic reform.
"I think my work and meeting could wait," one commuter told the BBC. "But our freedom, safety [and] human rights are being taken away and that can't wait - so I'm OK with it."
"I think it's OK because the government should respond to the demands of the citizens," another said.