The clashes began at the K C Road in Talapady last night.
While a group of persons were preparing the buntings ahead of a 'Brahma Kalashotsava' at the junction, another switched off the street lights and started pelting stones. The other group also retaliated with stones, police said.
Members belonging to both groups and three cops were injured in heavy stone pelting. They had been admitted to various hospitals.
Some persons also set fire to 13 shops in nearby Thokkottu. The shops were completely destroyed before the fire force personnel could reach the spot, police said.