The incidents are said to have taken place inside lifts in Tampines and Pasir Ris.

The Chinese man is in his late 20s and about 1.65m tall. He is fair-complexioned, plump with small eyes and has, black, spiky hair.

Police said on Wednesday he was usually seen in a round-necked striped T-shirt and bermudas.

He had also been spotted wearing a pink T-shirt in some instances.

Anyone with information should call the police at 1800-255-0000.

'All information will be kept strictly confidential,' said the police.