“They suddenly felt sick and got headaches,“ said Keo Pisey of the local police, reported news agency TT.
According to police, almost 240 workers suddenly lost consciousness on Monday and Thursday. This is the third time this year something similar happens in the clothing chain's affiliated factories.
“I was shaking, I couldn't breathe and I vomited. Many vomited,” said 29-year-old Chea Chanry, one of the affected, to news agency Reuters.
The company which operates the factory, Anful Garments Company in the Kompong Speu province, located about 50 kilometres from the nation's capital Phnom Penh, has recently been using chemicals to get rid of cockroaches, reported the local police.
About 136 employees fell ill on Thursday when the workers returned to the factory after a three-day closure following about 100 other staff fainting on Monday.
H&M said that it had started an investigation into why workers are fainting and is interviewing the employees about their experiences.
"The workers' wellbeing is of importance to us, and we are concerned about the situation at the suppliers," H&M said to Reuters.
Several other large clothes manufacturers operating in the country have experienced similar incidents and mass faintings have occurred twice already this year at two other suppliers of H&M garments in the region.
The Cambodian textile industry employs around 300,000 workers and grew by 28 percent last year. Most of the factories are owned by Chinese or Taiwanese companies.
The workers are mainly low paid women and the unsatisfactory working conditions have led to a slew of strikes and protests in the last few years.