Firefighters tackling the blaze at a Hertfordshire oil depot have resumed work after a pause amid safety fears.
Crews had left the site earlier and the M1 was shut, as experts ensured a fuel tank was not at risk of exploding.
Police hope the fire can be brought under control by Tuesday morning. It began on Sunday and has injured 43.
The M1 reopened but the M10 is closed. Schools within a 10 mile radius will be shut on Tuesday and 36 families were spending the night away from home.
Latest satellite imaging showed an immense column of smoke still pouring out of the Buncefield depot, stretching for more that 70 miles across southern England and heading for France.
Around 150 firefighters from several services across England will be working at the site overnight. Fires in 12 of the 22 plant tanks were put out on Sunday.
One person admitted to Watford General Hospital in intensive care with respiratory problems has been stabilised. Another person in Hemel Hempstead Hospital was reported to be under observation.
People in the area have been advised to keep their windows and doors shut and some of the 2,000 evacuated have been unable to move back into their properties.
Earlier, Deputy Prime Minister John Prescott told the Commons the government would provide support and assistance after the fire, said to be the largest of its kind in the UK and Europe during peacetime.
What's what at the Buncefield storage depot
He said the explosion was thought to have been an accident but a full investigation would be carried out by the Health and Safety Executive in due course.
The plume of smoke was not toxic, he said, but was "certainly unpleasant and may affect people with lung conditions".
The government was working with agencies to get the most up-to-date information available about the implications for public health, he added.
The Met Office said the heat from the fire had lifted the plume to a high altitude and that a north-easterly wind had meant it now reached as far as Dorset.
BBC forecaster Dan Corbett said the winds would remain north-easterly at about 5-10mph overnight.
Hertfordshire Fire Service said its operation to smother the fire with a foam blanket had reached a "critical phase" as crews moved on to the larger fires at the depot.
The operation had waited until firefighters gathered sufficient supplies of foam concentrate from around the country.
It uses six high-volume pumps and foam is combined with 32,000 litres of water per minute, much of it from a nearby lake.
Measures are being taken to stop pollution of the water table and river, with firefighters at the site trying to keep waste water in contained areas.
The Food Standards Agency said there currently appear to be no immediate concerns about contamination to crops or dairy herds.
Oil firm Total, which operates the depot, has set up a telephone hotline - on 0870 400 0499 - to enable those whose properties have been damaged to log their details.
Police officers - including anti-terrorist detectives - are investigating the disaster, but say there is "nothing to suggest" it was anything other than an accident.
And a spokesman for Total denied there had been leaks in the run-up to the explosions.
The Buncefield depot is a major distribution terminal operated by Total and part-owned by Texaco, storing oil and petrol as well as kerosene which supplies airports across the region, including Heathrow and Luton.