JOHOR BARU • A chemical plant in the industrial town of Pasir Gudang that was identified as the source of a chemical stench which engulfed parts of Singapore has been issued a stop work order by the Johor Department of Environment (DOE).

"The order will be in effect until the plant completes necessary remedial actions. We will make sure that the plant complies with the order before allowing it to resume operations," the DOE director, Datuk Dr Mohammad Ezanni Mat Salleh, told the New Straits Times.

He said the order was issued in the wake of a fire at the plant earlier this month.

Singapore's National Environment Agency (NEA) had contacted the DOE for assistance after residents complained of an acrid, chemical stench on Monday.

Complaints first poured in from residents in Sengkang and Punggol, and later in estates such as Ang Mo Kio, Yishun, Seletar and Bishan. Thick smoke also hung over some of the affected areas, residents said.

A large zone in the 311 sq km town of Pasir Gudang is dedicated to heavy industries, and fumes and pollutants have drifted to Punggol in past incidents.

The industrial estate, established in the 1990s, is a little more than 1.5km across the Strait of Johor from Punggol, and controlled burning to get rid of waste gases is a common occurrence there.

The town is home to a port, power station and petrochemical companies, and those dealing in edible oils, steel and fertiliser.

Some in Singapore affected by the stench were worried that the gas might be toxic, but the NEA has assured the public that air monitoring stations detected only low and safe levels of volatile organic compounds (VOCs).

VOCs are chemical compounds that easily enter the air.