A large amount of energy was suddenly released, and two explosions ruptured the reactor core and destroyed the reactor building. One was a highly destructive steam explosion from the vaporising superheated cooling water; the other explosion could have been another steam explosion or a small nuclear explosion, akin to a nuclear fizzle. This was immediately followed by an open-air reactor core fire that released considerable airborne radioactive contamination for about nine days that precipitated onto parts of the USSR and western Europe, especially Belarus, 16 km away, where around 70% landed, before being finally contained on 4 May 1986. The fire gradually released about the same amount of contamination as the initial explosion. As a result of rising ambient radiation levels off-site, a radius exclusion zone was created 36 hours after the accident. About 49,000 people were evacuated from the area, primarily from Pripyat. The exclusion zone was later increased to radius when a further 68,000 people were evacuated from the wider area.