Arriving on social visit passes, they don religious robes in the morning and make their rounds, the newspaper said. Many then shed their robes and emerge in civilian clothing, heading for nearby coffee shops.
A large group made a quick exit after police were seen near their lodgings. After exchanging Singapore currency for Thai baht, they boarded coaches headed for Malaysia.
"I am scared I'll get arrested," the newspaper quoted a 21-year-old man as saying. "If I am thrown in jail, I will have no future."
Anyone who collects alms or solicits charitable contributions under false pretences can be fined up to 2,000 Singapore dollars (1,315 US dollars) or jailed up to three months, or both.
The fake monks operate from syndicates which are based in Johor in Malaysia and Hatyai in southern Thailand, said a spokesman for the Thai Buddhist Temple in Singapore.
The gang leaders work closely with their partners in the city-state, who pocket 30 per cent of their collections, he added.
A fake monk can make as much as 800 Singapore dollars (526 US dollars) a day, but usually the amount is far less.