YEREVAN — 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, happening early afternoon, killed at least five people, injured 60 others and sparked a huge fire that raged into the night, according to the country's Ministry of Emergency Situations.

Nineteen more people are unaccounted for as of Monday morning, with relatives believing they could still be trapped in the wreckage of a building destroyed by the blast.

The cause of the explosion remains unknown.

Rescue workers and volunteers searched amid still-exploding fireworks, pulling dead and injured people from under slabs of concrete and twisted metal throughout Sunday.

The victims are four women and a man.

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.

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 AP reporters 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.

Rescuers used diggers to clear large piles of steaming rubble from the demolished building in an attempt to find survivors.

Many volunteers also got involved, shifting piles of heavy concrete and twisted metal by hand.

"I have never seen anything like this in my life, this is the first time I see such a thing," said local resident Arsen, who did not give his surname.

According to Armenia's Ministry of Emergency Situations, some 200 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, smoldering ruins.

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

The embassy of Russia, a neighboring 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. — Agencies