"The army has been deployed to maintain order. They have also been deployed at police stations to prevent mobs attacking them," said an officer, who declined to be named.
A 22-year-old factory worker died in hospital Wednesday after being critically wounded in a police shooting two days earlier during demonstrations against the government's proposed pensions reform.
The top police officer for Katunayake quit Wednesday, taking responsibility for the use of live ammunition in the police firing that also wounded over 150 workers.
A media report said that German-owned factories were among those damaged during a rampage that saw machinery destroyed.
Sri Lanka's main opposition political parties have blamed the government for the brutal crackdown.