HONG KONG — A brazen overnight attack by a mob of men with sticks and metal bars who were apparently targeting antigovernment protesters raised tensions in Hong Kong to new levels on Monday after weeks of demonstrations, prompting fears of violence spiraling beyond the authorities’ control.

Dozens of people, including journalists and a pro-democracy lawmaker, were injured in the assault in and around a train station in Yuen Long, a satellite town in northwestern Hong Kong near the border with mainland China.

The violence followed clashes earlier in the evening between the police and protesters near the Chinese government’s liaison office in Hong Kong, and raised questions about why officers did not protect demonstrators, who have been critical of the police’s use of force in recent weeks.

Protesters painted graffiti on the Chinese government’s liaison office in Hong Kong on Sunday, and threw ink on the crest of the Chinese state displayed there, an act that Chinese officials said “openly challenged the authority of the central government.” Earlier, demonstrators participated in a peaceful march calling for an independent investigation into accusations of police brutality.