Protesters armed with clubs and metal bars stormed into the mayor's office of Almaty, Kazakhstan's biggest city, local news website Zakon.kz reported on Wednesday.
Videos posted online showed a crowd gathering outside the building amid smoke and stun grenade explosions.
Protests raged for a second day in the oil-rich Central Asian nation, triggered by a surge in car fuel prices. President Kassym-Jomart Tokayev has declared a state of emergency in the city and accepted the government's resignation.
An Instagram live stream by a Kazakh blogger showed a fire blazing in the mayor's office, and gunshots could be heard nearby.
Protests began in the west of the former Soviet republic on Sunday over fuel price increases, leading to the resignation of the government earlier on Wednesday.
"Extremists and radicals" are attacking Kazakhstan's biggest city, Almaty, and have beaten up 500 civilians and ransacked hundreds of businesses, the city's police chief said.
Police, National Guard and Army units are involved in the security operation in the city, police chief Kanat Taimerdenov said in a statement on the second day of clashes between protesters and security forces.
Kazakh President Kassym-Jomart Tokayev declared a state of emergency in the capital city of Nur-Sultan, his office said protests in several major cities that police struggled to disperse.Tokayev earlier declared an emergency in the city of Almaty and the surrounding province, as well as in the western Mangistau province.