COLOMBO (AFP) - Sri Lankan authorities shut down a detergent factory in the its business capital Colombo on Tuesday after more than 70 people were hospitalised following a suspected toxic gas leak, police said.

Police spokesman Ajith Rohana said 72 factory workers and nearby residents were taken to hospital earlier on Tuesday after gas - thought to be ammonia - leaked from the plant.

"Some of them are still in hospital eight hours after the incident was reported," Mr Rohana said.

"The initial investigations suggest there had been an ammonia gas leak from the plant," he said.

The Central Environmental Authority (CEA) said it immediately shut down the factory in the suburb of Piliyandala on the outskirts of Colombo pending further investigations.

CEA director Saranga Alahapperuma said investigations were underway into the factory's methods for storing chemicals used to manufacture detergents.

Industrial accidents are rare in Sri Lanka but there is growing concern about factories near residential neighbourhoods following a recent groundwater contamination by a rubber glove plant just outside Colombo, which triggered a protest that ended with a violent crackdown.