(Reuters) -About 6,500 people have been told to evacuate their homes in Winston-Salem, North Carolina, due to a fire at a fertilizer plant where 600 tons of potentially explosive ammonium nitrate was stored, city officials said on Tuesday. The blaze at the Weaver Fertilizer Plant started Monday evening. Residents within one mile (1.6 km) of the plant were urged to evacuate and stay away from their homes for up to 48 hours. Winston-Salem Fire Chief William “Trey” Mayo said during a news conference on Tuesday that 500 tons of ammonium nitrate and 5,000 tons of finished fertilizer were at the sit…