A fire is continuing to blaze at a fuel depot in Hertfordshire after a series of large explosions sent black smoke drifting up to 40 miles away. Investigation under way In total, 20 petrol tanks were involved in the fire, each said to hold three million gallons of fuel. Police say 43 people were injured, two of them seriously, after flames shot hundreds of feet into the sky. The first blast at 0603 GMT at the Buncefield fuel depot, close to junction 8 of the M1 motorway was heard more than 100 miles away. The fire, which police believe was an accident, could burn for another day. About 2000 people living nearby the Hemel Hempstead site have been evacuated, while police have advised others to keep their windows and doors closed because of fumes. Thick clouds of smoke are spreading to the south-east and south-west of the site. One person is in Watford General Hospital in intensive care with respiratory problems. Another person is in Hemel Hempstead Hospital being kept under observation. The other 41 people were treated for minor injuries and discharged. Earlier rumours a plane was involved in the incident were unfounded, said a police spokesman. Witnesses said another two explosions followed the first at 0626 GMT and 0627 GMT. Hertfordshire Police Chief Constable Frank Whiteley said: "There is still a possibility there could be further explosions."