Two people were killed and four others were injured in a gas explosion in a five-story apartment building in Murmansk city in northern Russia.Citing TASS, Xinhua reported that the explosion occurred at 16:55 local time. A part of the wall and a part of the roof collapsed, destroying three floors of the building."I was in the shop, when I heard a loud bang, walls started to shake. Rescuers came within minutes," Local citizen Roman said. Another witness said there was a "strong blast wave."More than 390 people and over 90 units of equipment are involved in the rescue effort.