At least 30 people were killed and dozens injured in an explosion and fire at a petrol station in Russia's Caucasus republic of Dagestan, the Emergency Situations Ministry said Tuesday.

A total of 102 people were injured and killed as a result of the incident, the ministry said on the Telegram messaging app.

Makhachkala, a city of over 600,000 residents on the Caspian Sea, is the capital of Dagestan, a Russian republic bordering Chechnya.

The explosion took place in the building of a car service station, where a fire had broken out during maintenance work, Russia's Investigative Committee said.

A criminal case has been opened to establish the circumstances leading up to the incident, it added.

The state-run TASS and RIA Novosti news agencies reported that the fire had been extinguished, citing Russia's Emergency Ministry.

The blast was heard shortly before 10:00 pm on Monday, Sergei Melikov, head of the Dagestan regional administration, said on Telegram.

An eyewitness quoted by the Russian daily Izvestia said the fire started in an area where cars were parked and spread to the petrol station.

"After the explosion, everything fell on our heads, we couldn't see anything anymore," said the eyewitness, who was unnamed.

A video released by Russia's Emergency Situations Ministry showed a group of firefighters trying to extinguish flames near burnt-out vehicles, as rescue workers examined the rubble of a building with flashlights.

The fire had spread over an area of around 600 square meters, the ministry said, adding that 260 firefighters were deployed.

A government Il-76 aircraft carrying medical equipment was dispatched to Makhachkala to evacuate the seriously injured to Moscow, it added.