Some residents in Sengkang, Hougang, Serangoon, Yio Chu Kang and Ang Mo Kio complained about an unpleasant smell in the air yesterday evening.

Some residents who called The New Paper said that the odour smelled "like toxic gas". Others said that the stench gave them nausea and headaches.

A Netizen living in Ang Mo Kio wrote on an online forum that his sister had an asthma attack and his father suffered from a headache, thanks to the stench.

However, the National Environment Agency told The New Paper that no toxic gases were detected.

The NEA received over a hundred calls regarding the situation. It was monitoring air quality and investigating the source of the odour. NEA also told The New Paper that it had contacted its Malaysian counterparts to check if any unusual odours had been detected in Johor.