At least four people were killed and dozens of others remained unaccounted for early Monday after a suspected gas explosion ripped through a 10-story residential building in the Russian city of Magnitogorsk.

The apartment block partially collapsed after the blast, which occurred as many of the residents were sleeping at around 6 a.m. local time (8 p.m. ET Sunday).

The aftermath of an explosion that rocked a residential building in the Russian city of Magnitogorsk. CHELYABINSK REGION GOVERNOR PRESS SERVICE / AFP - Getty Images

The Russian Emergencies Ministry said 48 apartments were damaged after seven stories of the building collapsed.

Russian President Vladimir Putin traveled to Magnitogorsk later on Monday, and was told in an meeting with regional governor Boris Dubrovsky that 35 people, including seven children, were still unaccounted for.

Rescuers searched the apartment building's ruins for survivors throughout the day. Up to 40 people could be trapped under the rubble, according to Emergencies Minister Yevgeny Zinichev.

Local officials also warned that two adjacent building blocks could be at risk of collapsing.

Magnitogorsk is located 1,050 miles east of Moscow in the southern Urals.