A popular market in the Armenian capital, Yerevan, was devastated by a massive explosion at a fireworks storage area on Sunday.

The blast at Surmalu market in the early afternoon killed at least six people, injured 60 others and sparked a huge fire that raged into the night, according to the country's Ministry of Emergency Situations.

Another 18 people are unaccounted for, with relatives believing they could still be trapped in the wreckage of a building that was destroyed by the blast.

The cause of the explosion remains unknown.

Rescue workers and volunteers are still searching amid still-exploding fireworks, using diggers to pull dead and injured people from under slabs of concrete and twisted metal on Sunday.

Armenia's General Prosecutor's Office announced overnight that it was opening an investigation into possible violations of "fire regulations" or rules around storing flammable products.

Prime Minister Nikol Pashinyan also visited the scene of the explosion on Monday morning, according to his press office.

The Surmalu wholesale market is traditionally very busy on Sundays. Eyewitnesses reported that the explosion occurred in an area where fireworks were stored, yet the authorities have not confirmed this.

"There is no information at the moment," Alen Simonyan, Chairman of the National Assembly of Armenia told The Associated Press on Sunday afternoon.

"There is no conclusion [on what caused the blast] yet, but most likely a violation of fire discipline or something like that."

Footage circulating on social media showed a thick plume of black smoke rising high into the sky, with the sound of small detonations crackling in quick succession in the background.

"I have never seen anything like this in my life, this is the first time I see such a thing," said one local resident Arsen.

According to Armenia's Ministry of Emergency Situations, around 350 firefighters and rescue workers were deployed to the scene, as well as several trucks and construction machinery. They used long water hoses and ladders to extinguish the flames, leaving blackened, smouldering ruins.

The market, two kilometres south of the city centre, is popular with locals for its low prices and variety of goods.

The embassy of Russia, a neighbouring country of Armenia, indicated on Sunday evening it was seeking to establish whether Russians were among the victims.

"We express our sincere condolences to the families and loved ones of those who died in the explosion," it said in a statement.