Eyewitnesses say the fight which took place in the middle of the road blocked vehicles from entering or leaving Sentosa.
Vietnamese tourist Dung Troc, who recorded this video, says at least 3 to 5 people were lying on the ground unconscious and were sent to hospital.
He said that police eventually dispersed the crowd.
Sentosa Gateway is flanked by Vivocity shopping mall, and popular watering hole St James Power Station.
The incident happened at about 6am yesterday (10 Feb).