It is "not acceptable" for a major expressway to shut down due to flooding, Minister for the Environment and Water Resources Vivian Balakrishnan said on Thursday evening. Dr Balakrishnan was speaking to reporters on the sidelines of a research function at the National University of Singapore.

"We're going to need to do some work there," he said. "We will need some time, but I am confident that we can make an improvement to the situation...I told (national water agency) PUB we've got to do our best to make sure this doesn't recur in the future."

In the longer term, he said, there is the option of building a barrage along the canal, which opens to the sea, to control water and tidal levels in anticipation of flooding.

He added that the culvert beneath Clementi Road which leads to the Sungei Ulu Pandan canal, which also overflowed, will have to be expanded as well.

"These are problems that need to be resolved. They can be resolved," he said.

The Ayer Rajah Expressway (AYE) was one of the areas worst hit by Thursday morning's flash floods, which were caused by heavy rain falling over central and western Singapore. All four lanes of the AYE towards East Coast Parkway (ECP) were closed as flood waters reached a depth of 0.5m. The flood waters subsided within 40 minutes.