Protesters began disrupting city transit as early as 7 a.m. local time, as part of their day-long general strike.
They built barricades and blocked roads in several locations, including the crucial cross-harbor tunnel that connects Hong Kong Island with Kowloon. Police said demonstrators also blocked roadways in Sha Tin, Tseung Kwan O, Tuen Mun, and Hung Hom districts.
Several subway lines experienced minor to severe delays, with some stations closed and routes partially suspended "due to an escalation of the situation in stations," according to the MTR subway operator.
Most of the closed stations and suspended subway service are located further outside the city center -- in the New Territories, Lantau Island, and Tseung Kwan O.
In a statement in the morning, police said they were continuing to clear barricades and disperse the protesters.