Hong Kong police are suggesting a small-scale riot which broke out earlier this week was planned in advance.

Hong Kong police Commissioner Lo Wai-Chung says the investigation is suggesting the rioters were bused in.

"It was an organized and planned riot. Police forces in Hong Kong are going to continue to strictly enforce the law, and plan to make further arrests. I want to ensure people in the city that Hong Kong police have ability and confidence to handle any illegal acts, and will be doing our best to ensure that those behind the rioting will be found."

A mele broke out on Monday evening during the Lunar New Year's celebrations in the bustling Mong Kok district in Kowloon after police attempted to clear out illegal street vendors.

Hong Kong Chief Executive CY Leung says those responsible will be punished.

"The Government of the Hong Kong Special Administrative Region severely condemns the violent behavior of the rioters. We will never tolerate this. Hong Kong police are not going to spare any effort to arrest those responsible. Meanwhile, I would like to deliver my sympathy to the police officers and news reporters injured in the riot."

Rioters in Mong Kok hurled bricks and stones at police officers during the rioting, which lasted for a few hours on Monday evening and early Tuesday morning.

Around 300 people were involved.

Over 90 police officers and 4 reporters were injured in the unrest.

Police arrested 54 people that evening, and expect that number to rise as the investigation continues.