The attackers broke into the Leader Publications' printing section in suburban Colombo around 2:00 a.m. ( 20:30 GMT Tuesday) and ordered the workers to kneel down outside before setting fire to the machines, said company head Lal Wickramatunga.
The company publishes The Sunday Leader, The Morning Leader, a weekly newspaper and a Sinhalese-language Sunday newspaper, all articulating critical views of President Mahinda Rajapakse's government and offering support for the opposition.
Wickramatunga did not name any possible suspects.
Police spokesman Jayantha Wickramaratne said initial investigations have not uncovered those behind the attack.
A gang burnt down the same printing section two years ago and the case remains unresolved, Wickramatunga said.