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In this photo provided by the Yaroslavl Branch of Russian Emergency Ministry Press Service, emergency and rescue workers search the debris of a 5-story apartment building after a powerful natural gas explosion early Tuesday, Feb. 16, 2016, in Yaroslavl, Russia. Image Credit: Russian Emergency Ministry Yaroslavl Branch Press

Moscow: At least seven people were killed and more than 30 people were reported trapped after a powerful gas explosion triggered the collapse of a five-storey residential building in Russia's Yaroslavl city early Tuesday.

Preliminary information showed that about 10 flats on the first to fifth floors of a single unit of the residential structure fell apart in the blast, the Russian emergency situations ministry said.

Up to 39 people were estimated to be buried in the rubble, according to the ministry, which added that fire fighters had rushed to the site for search and rescue operations after being alerted at 4.20 a.m., Xinhua news agency reported.

The ministry estimated that between seven-20 people could have been in the building at the time of the incident. Out of those officially registered in the ten apartments, 13 are reported to be minors.

So far, four people have been rescued from the debris, RT news reported.

All of those rescued reportedly suffered serious injuries and fractures and were hospitalised in a critical condition.

The explosion did not trigger any big fire, but authorities cautioned that they could not rule out the possibility of further collapse of the building.

The ministry warned of more casualties.