One of the girls was offended by their forwardness and complained to her boyfriend.
The angry boyfriend then went and called out 20 men, believed to be part of a local secret society, and went for the kill.
They armed themselves, some with knives, and stormed the club.
The 4 Singaporeans were injured badly.
One of them was even hacked and needed to be sent to hospital.
The incident happened at about 3am, at a club in Kluang.
Police have arrested 5 people related to the incident.