The blaze reportedly started inside a pavilion.

According to the UN, the fire was extinguished within six minutes, and 13 people received treatment for smoke inhalation. The cause of the fire is not yet known, the BBC reported.

"It was climbing the walls and onto the ceiling. People were screaming," Dr. Harshita Umesh, who was giving a talk next to the location where the fire broke out, told BBC News.

"Then I ran, I think I tripped and fell," Umesh said.

Dr. Umesh, a medical doctor, said ambulance staff told her that first responders inhaled “toxic fumes” and were given oxygen masks at the site.

Emergency medicine specialist Kimberly Humphrey, who is currently helping patients at the COP medical centre, told the BBC the injuries were “mainly people with smoke inhalation, someone with a lung injury from smoke.”

"People are pretty traumatised and shocked," she added.

One eyewitness told the BBC he believes an electrical fault caused the fire.

Thousands of delegates from around the world are attending the event, where nearly 200 countries are discussing ways to advance efforts to tackle climate change.