Shah Alam district police chief Iqbal Ibrahim said authorities were alerted by a resident of the housing area, who complained of a foul smell from a drain nearby at about 9.30pm.

Iqbal said police and the Selangor fire department’s Hazmat unit found that the odour, suspected to be ammonia pollution, originated from a drain near a warehouse.

“The warehouse management said regular maintenance works were being carried out as scheduled but they were unaware of any blockage to the drainage system causing odour pollution,” he said in a statement today.

Iqbal said the fire department used the fire hydrant at the warehouse to flush the drainage system to reduce the odour to a “safe level”.

A resident, who wished to remain anonymous, said about 40 to 50 houses at Berjaya Park were affected.

He told FMT the residents were asked to evacuate at about 10pm and to only return when the authorities had considered it safe to do so.

He said he received an update two hours later after he had approached the fire department personnel at the scene.

According to him, some residents were forced to spend the night elsewhere as they needed to go to work this morning.

FMT has contacted the company concerned for comment.

In a separate statement, Selangor police chief Hussein Omar Khan said the fire department’s investigation found that ammonia gas had leaked when maintenance work was being conducted on the warehouse’s cold storage piping system.

He said the situation was under control and that there were no injuries, adding that the fire department’s Hazmat unit will return to conduct further checks tomorrow morning to ensure no pollution is detected.