A blast rocked an optics and optical electronics factory in the town of Sergiev Posad, 50km northeast of Moscow, injuring at least 45 people, local authorities have said.
Emergency services said this morning's blast appeared to have occurred in a warehouse containing pyrotechnic equipment, the state news agency TASS reported. The popular online news channel Mash said it had been rented by a pyrotechnics firm.
So far, 23 people have been admitted to hospital, including six in intensive care, the Sergiev Posad mayor's office said.
Unverified footage on social media showed a huge column of smoke, and high-rise buildings with windows blown out.
The Zagorsk Optical and Mechanical Plant produces optical equipment for industrial and healthcare applications as well as for the Russian security forces.
However, TASS cited emergency services as saying they did not believe the blast had been caused by a Ukrainian drone attack - many of which have taken place in Moscow and the surrounding area in recent weeks and months.
Earlier today, Russian forces shot down two combat drones headed for Moscow, the city's mayor said this morning.
"Two combat drones' attempt to fly into the city was recorded. Both were shot down by air defence," Moscow mayor Sergei Sobyanin said on Telegram, without naming an attacker.
He said one drone was downed in the Domodedovo area on the southern outskirts of the city, while the second was shot down in the Minsk highway area, west of the capital.
"At the moment, there is no information about victims of the fall of the wreckage," he said, adding that emergency services were on the ground.
The strikes are at least the third attack on Moscow within a week, with Ukrainian drones downed on Sunday and Monday, according to Russian officials.
Moscow was rarely targeted throughout the conflict in Ukraine until several attacks this year.
Russia's defence ministry said last Thursday it had downed seven drones over the Kaluga region, less than 200km southwest of Moscow.
On 30 July, Ukrainian President Volodymyr Zelensky warned that "war" was coming to Russia, with the country's "symbolic centres and military bases" becoming targets.
At the start of this month, an office block in the capital's main business district was struck twice within days by debris from a downed drone strike.
