Two people were killed and six injured when a gas explosion ripped through a five-storey residential building outside Moscow on Saturday, with rescue workers still looking for survivors.

The blast took place in the town of Orekhovo-Zuyevo during stay-at-home orders aimed at slowing the spread of the coronavirus.

The emergencies ministry said two people were killed and another six were injured when a section in the middle of the brick building collapsed in the town north of the capital.

Rescue workers were combing the debris as two more people could be under the debris, head of the emergencies ministry's Moscow region branch, Sergei Poletykin, said in televised remarks.

Ten flats have been partially destroyed and officials were trying to establish how many people lived there.

The rest of the building appeared intact.

National television broadcast footage of mangled heaps of concrete as locals — some wearing masks — gathered at the scene.

All residents of the damaged building have been moved to a school nearby, officials said.

Gennady Panin, head of the Orekhovo-Zuyevo city district, said earlier that six people had been pulled from the debris.

Three people, apparently from among those six, were in intensive care, he added.

Witness Alexei Muranov, who lives near the damaged building, said he stood near the window when he was pushed back by a shock wave.

"At first things were not clear, it looked like a car blast, there was a little bit of smoke," Muranov said in televised remarks.

"And then people ran there," he said, adding that several floors had collapsed. "Only a roof has remained."

The Investigative Committee said the gas explosion took place on the third floor of the building.

Investigators said they were looking into the cause, with a gas leak and damaged gas equipment believed to be among top leads.

Moscow region governor Andrei Vorobyov and emergencies minister Yevgeny Zinichev immediately went to the scene.

Gas explosions are common in Russia and often affect residential buildings built in the Soviet era.