Police have arrested the manager of the Horana factory where an industrial accident saw 5 employees being died.
The incident happened at around 1.20 this afternoon.
Police said first a worker had fallen accidentally into an ammonia tank and then other colleagues have attempted to rescue him.
As a result, 5 other workers also died after inhaling the toxic gas.
The workers were admitted to the Horana Base Hospital.
Around 34 persons are now in hospital.