Firefighters will continue working into the weekend at the side of a huge industrial blaze in Essex.The fire, which prompted the evacuations of nearby residents, was declared a major incident on Friday afternoon.Emergency services were first alerted to the inferno on Southend Road, between East Hanningfield and Rettendon, at 4.50pm on Friday, the Essex County Fire and Rescue Service said. Several industrial units and an adjacent field were engulfed in flames.Area manager Dave Bond said that fertiliser exploded within one of the units while crews were present.Smoke billows from a fire at an Essex industrial unit (Reuters)Residents have been evacuated as a precautionary measure, although Mr Bond said that all personnel at the scene remain safe.About 100 firefighters have been deployed to combat the extensive fire, with dozens expected to remain on site into Saturday.Mr Bond said in a video update at 10.45pm Friday: “We’re still at the scene of a significant fire in East Hanningfield.“As you can see behind me, we’re still dealing with significant spots of fire. However, we do have this incident under control and surrounded.“We’re in the process of scaling back, but we do still have 50 firefighters on scene. We’re still working closely with our partners, including police, ambulance, utility companies, and we also have a number of specialist advisers on scene, giving us support as we move through the night.”Firefighters will remain at the scene of an industrial unit fire in Rettendon, Essex (PA Wire)Mr Bond said that the incident will be “ongoing into the weekend”.He asked people to stay away from the area so that firefighters can continue their operations.“We apologise for any inconvenience this caused, and we thank you for your patience,” he said.“The advice we’re still giving to the public is that if you do smell smoke, then close your doors and windows. But please bear with us as we continue our operations to extinguish the fire.”A spokesman for East of England Ambulance Service said it had declared a critical incident and its hazardous area response team was in attendance.Smoke plumes could be seen billowing in the sky in photos and videos posted online, while some locals have said they heard explosions.