This is the moment armed police freed dozens of people who were hiding in rooms in a Thailand shopping mall where a gunman is holding hostages.

The terrified shoppers and staff from the Terminal 21 building in Nakhon Ratchasima, northern Thailand, had fled into rooms and stores when the killer entered the building at around 6pm local time.

They had spent around six hours fearing for their lives before police SWAT teams entered the building and helped to release them.

A lone undercover cop is also inside the mall beckoning the killer, Sergeant Major Jakrapanth Thomma, into the open - even exchanging threats with him. The decoy has allowed those hiding in rooms on the ground floor to escape.

The gunman is believed to have killed at least 20 people and seriously injured 40 others during the rampage, which he broadcast on Facebook.

Relieved photographer, Chatsurang Kongph, 30, who was locked in one room with several other people, filmed people streaming out of the building after she herself escaped.

She said: ''Nobody knew if we were going to get out alive. The shooter could have came into our room at any moment and killed us all.

''Everyone was afraid to make a sound and we kept the light out.''