Firefighters say they hope to extinguish the massive Buncefield oil depot blaze by the end of the day.
Only three of the huge oil tanks are still on fire and officials said real progress had been made overnight.
More than 150 firefighters have been battling to douse the blaze, which began following a series of explosions at 6am on Sunday.
A spokeswoman for Hertfordshire Police said: "It has been a demanding night but real progress now looks to have been made."
She said fire crews pulled back from the blaze briefly at one point overnight when a tank suffered a "structural failure" which was thought to pose a risk to other tanks nearby.
The "cooling patrols" had been successful and crews were this morning concentrating on extinguishing the final three tanks.
"Despite the still spectacular emissions coming from the site, the public can be reassured that the fire remains under control," said the police spokeswoman.
Roy Wilsher, chief fire officer of Hertfordshire Fire Service, said firefighters were facing "very harsh" conditions. Wind was swirling the dense smoke and hampering their efforts.
He said the fire was the largest of its kind seen in the UK and Europe in peacetime."
Source
Only three of the huge oil tanks are still on fire and officials said real progress had been made overnight.
More than 150 firefighters have been battling to douse the blaze, which began following a series of explosions at 6am on Sunday.
A spokeswoman for Hertfordshire Police said: "It has been a demanding night but real progress now looks to have been made."
She said fire crews pulled back from the blaze briefly at one point overnight when a tank suffered a "structural failure" which was thought to pose a risk to other tanks nearby.
The "cooling patrols" had been successful and crews were this morning concentrating on extinguishing the final three tanks.
"Despite the still spectacular emissions coming from the site, the public can be reassured that the fire remains under control," said the police spokeswoman.
Roy Wilsher, chief fire officer of Hertfordshire Fire Service, said firefighters were facing "very harsh" conditions. Wind was swirling the dense smoke and hampering their efforts.
He said the fire was the largest of its kind seen in the UK and Europe in peacetime."
Source