Hundreds of people were evacuated from their homes close to the fuel depot and are sheltering at a nearby leisure centre.
Residents from Barleycroft, Leverstock Green, have gathered at Jarmans Park on the outskirts of Hemel Hempstead.
People have brought their pets but very few have come with a change of clothes and everybody does not know what is going to happen.
Dominic and Sheila Gizzie, who live near a cemetery only a quarter of a mile from the blast site, said they thought there may have even been an earthquake.
Mr Gizzie said: "We got woken up this morning with a huge explosion.
"We have a lot of damage, our fireplace was blown out, several doors came off and the garage door has broken."
His wife added: "I have never heard such a loud explosion in my life, we did not know what it was, we have recently come back from New Zealand so we thought it may have been an earthquake."
The retired couple ran to their windows to see what was going on.
Mr Gizzie said: "The flames were 100ft into the air. I have never seen anything so big."
The couple were told by police that they must evacuate their house in case another explosion occurred.
Police fear that the fire may catch gas pipes underneath the houses, leading to yet more explosions.
Mrs Gizzie, who was holding her dog lead as she spoke, said they had no idea what was going to happen to them.
"We were so shaky this morning, we had such a fright - you do not expect to wake up and have an explosion at your door," she said.
"We just don't know what is going to happen."
Maureen Talbert, from Barleycroft, was fast asleep when the blast threw her from her bed.
The 65-year-old looked out of her window and saw flames shooting into the air.
" Like most people, I thought a plane had crashed and everybody was running into the street to have a look."
Mrs Talbert was evacuated to the centre while more than 200 firefighters attended the scene.
They are not trying to quell the flames - instead letting the fuel burn out.
At the centre, pizzas were being handed round to the evacuees and emergency service staff.
Scores of people huddled around television screens to try and find out what had happened.
Sandra, aged 55, and Peter Cockran, aged 56, from Leverstock Green, were evacuated from their house less than an hour after the first explosion.
Mrs Cockran, who works on the switchboard at BT, said their patio doors had shattered and all their cupboards had blown out.
The couple are concerned about security, because their house - which they have lived in for 20 years - is now open to the elements. Along with their 13-year-old daughter Nadine, the Cockrans do not want to leave the leisure centre because they fear this is the best place to get information.
Mrs Cockran said: "We just want to see what they come up with, we want to know when we can go back to our house.
"We know they are not letting people return at the moment because they are worried about the fumes."
She went on: "We are all feeling a little bit shaky still, we want to go home but we just don't know how long it will take."
Helen Glass, from Leverstock Green, was sheltering at Jarmans Park with her two children, Megan, aged nine, and William, aged six.
The 36-year-old said: "There was just a massive explosion and a long rumbling sound - at first I thought it was a gas explosion or that a plane had crashed.
"Both children came running into my room and were absolutely terrified."
Mrs Glass and the children looked out of the window and saw flames shooting into the sky.
Megan said: "I was really shocked and scared by what we saw - the radiator in my bedroom fell off the wall and a mirror cracked."
The family was quickly evacuated and do not know where they would go if they have to stay away from home.
Mrs Glass said: "We just have to sit here because we don't know whether we will go back tonight or tomorrow - I hope it is tonight.
"The children are very excited at being at the leisure centre because they have been given pizza and told that the ice rink will be open for them to use."
She added: "I am worried about my house but there is not a lot we can do at the moment, if it is going to happen it is going to happen.
"Before we left the house we lowered all the blinds so if another explosion occurs hopefully the glass will be contained."
Mrs Glass said she was shocked and wanted to know what had caused the blast.
"I want to know when we can go home and I want to know why this happened and if it could happen again," she said.
By 4.30pm, 290 people had registered themselves as evacuees, and around 50 families were being put up in bed and breakfasts.