The explosion hit the 20-floor tower block at around 10:40 p.m. local time (19:40GMT) on Saturday, damaging apartments on the upper floors.
"A man born in 1941 has died in hospital," Alexandru Pinzari, the chief of the Ministry's general police inspectorate, told reporters at an emergency meeting.
Liliana Puscasu, a spokeswoman for the general inspectorate for emergency situations, said bodies of a woman and a child were found under the rubble on the 14th floor.
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Seven people were taken to a hospital, including a rescuer whose condition Puscasu described as "satisfactory." A search is underway for more people who may have been trapped under the debris.
Pinzari said remnants of a gas cylinder were found on the 16th floor, believed to be the "epicenter of the blast," seemingly confirming suspicions that the explosion was caused by compressed gas.