At least 20 people were injured on Tuesday after industrial police used batons and sound grenades to disperse about 500 garment workers who blocked Dhaka-Mymensingh highway at Cherag Ali point in Tongi, eyewitnesses said.

The workers threw brickbats at police during the clash that halted traffic on the highway for about three hours, eyewitnesses said.

At least five policemen were among the injured, a police officer said.

The workers from Gooryong Fashion Limited were protesting against the factory authority’s show-cause notices to 28 of their colleagues and firing of several others for what they said without any reason earlier on Monday.

The infuriated workers took to the streets when on Tuesday they found a notice at the main gate of the factory announcing its indefinite closure.

To clear the demonstrators police charged batons and fired sound grenades to disperse them, triggering a chase and counter chase.

Vehicular movement returned to normal three hours after the incident as police brought the situation under control.

S Alam, assistant superintendent of Tongi Industrial Police-2, said five policemen were injured in the incident. They were given first aid.

The authorities concerned of the factory declared to suspend the production of the factory for an indefinite period following the unrest.