A huge blaze which broke out at a power station in Essex, in an area containing about 4,000 tonnes of wood pellets, is still being tackled by firefighters.
There was concern about the structure of the building at Tilbury Power Station, as water sprayed on the pellets was increasing their weight.
But firefighters have since gone into the heart of the blaze with foam spray to deprive the fire of oxygen.
Plant owners RWE npower said: "All our employees have been accounted for."
Essex chief fire officer David Johnson said it was proving "physically and technically challenging" to bring the fire under control but this could be achieved by mid-afternoon,
"We were able to establish it (the building) was safe so we put a few crews in."
They reported back on the conditions they found.
"We're applying specialist high-expansion foam which we hope will starve the fire of oxygen. This won't cause the structural problems that putting water on it would.
"It's very hot and it's very smoky in there and we still have fears for safety should the building collapse.
"Assuming our tactics work, the bulk of the fire should be extinguished within the next two or three hours.
"Then it's about whether the fuel is continuing to burn within the hoppers under the foam blanket - that could take anything up to about a day or two to extinguish.
"This is a hugely challenging fire. I've only been to another one of this kind once before in my 24-year career."
More than 120 firefighters, 15 fire engines, three aerial ladder platforms and a mass foam attack unit have been tackling the fire.
'No dangerous chemicals'
Extra fire crews were called in from London and further afield to deal with a separate unrelated fire in a wood pile on a nearby dockside.
Talking about the power station fire, witness Robert Richards told BBC Essex: "The whole of that north block just went completely up in flames.
"It was on two sides that I could see. My daughter could see it from the other side of the river."
Tilbury Power Station was built to burn coal but was recently granted consent to burn biomass fuel and wood materials.
Biomass plants burn wood pellets, generally made from compacted sawdust or other wastes.
Mr Johnson said it was too early to say what caused the blaze.
"Thankfully nobody has been hurt," he said. "We initially believed there were personnel from the power station missing but all have been accounted for, so everyone is safe," he said.
"The smoke that's being given off is very similar to what you get from a bonfire, there are no dangerous chemicals involved, no pipes or liquids involved."
John Kent, leader of Thurrock Council, praised the efforts of fire crews.
"Because it's in the process of being converted [to biomass], there shouldn't be any lasting impact to the National Grid and no shortage of power as a result," he said.
"We just have to wait until the fire is under control and see what the situation is and how much damage has been done. "
Nigel Staves, power station manager said that it looked like only the north end of the power station was affected.
The power station has already begun an investigation into the cause of the fire, which is likely to last several weeks.
"Until we can actually get in to see the damage and understand what happened we have no idea how the fire started at the moment," Mr Staves said.
"The bunkers are very strong, made of strong steelwork, designed to hold 1,000 tonnes of coal.
"Until we can assess how many of the bunkers were on fire it will be difficult to say how much damage we have, but I'm hoping it is more superficial."
He hoped power could be generated from the unaffected south end of the site, possibly once the fire was out.
"It could be two or three days, it could be a week. It will depend on the investigation when we go in and see the damage," he said.
Tilbury supplies the National Grid with less than 1% of the total electricity production in the UK.
"As soon as we shut the power station down this morning, another power station was started to replace that energy. That will continue until we get Tilbury back on-line," Mr Staves said.
A "minimal" number of staff remain on site in the control room working alongside the firefighters.