Image copyright PA Image caption Rescue workers are searching the blast site for four missing people

Rescuers searching for four people missing after an explosion devastated a mill are focusing on two areas identified by sniffer dogs.

The four-storey Wood Flour Mills in Bosley, near Macclesfield in Cheshire, collapsed after the blast on Friday.

Some areas are still alight while dogs have been used to help search for the three missing men and one woman.

Cheshire Fire and Rescue Service said they were also working to protect what could potentially be a crime scene.

'Always hope'

The missing people were believed to have been in the building and near the seat of the explosion that ripped through the wood treatment works shortly after 09:00 BST.

Chief fire officer Paul Hancock said: "There's still hope but the longer the incident continues without knowing or locating these four individuals, it is looking more like a recovery than a rescue operation.

"Until we account for them there's always hope."

Mr Hancock told reporters: "We have identified two locations we are now focusing on. These locations have been confirmed by sniffer dogs.

The rescue teams have experience working in the aftermath of earthquakes in Nepal, Japan and the Christchurch earthquake in New Zealand.

Image copyright PA Image caption The teams have experience working in disaster zones including earthquakes in Nepal and Japan

Image copyright News helicopter still Image caption Macclesfield MP David Rutley said there was a "really deep sense of shock" locally

On Friday, 35 people were assessed at the scene with four people treated for breathing difficulties and another four people taken to hospitals in Birmingham, Merseyside and Stoke.

One 29-year-old woman sustained serious burns and blast injuries to her head, face, arms and chest.

Firefighters are continuing to use water to cool silos on the site and assess temperatures using thermal image cameras, a spokesman for the fire service said.

They will be working alongside Cheshire Police and the Health and Safety Executive to establish the cause of the blast, he added.

At the scene: Judith Moritz, BBC North of England Correspondent

Up close, the devastation is clear - wreckage strewn across a wide area, the mill building a collapsed shell. Search teams who are used to working in earthquakes are combing through the rubble piece by piece using specialist cameras to capture images below the surface.

Search dogs are also scrabbling over the ruins concentrating on an area where the four missing people are thought to be. Meanwhile, huge water jets can be seen trained on parts of the complex which are still alight with gallons of water being pumped out of the stream which runs alongside.

Firefighters say the temperature of one of the mill silos is still 140C. They say they expect to be working at the Cheshire site for several days.

The Conservative MP for Macclesfield, David Rutley, said there was a "really deep sense of shock" locally.

"It's something that's affected most people who live in the village, because they all know somebody that works there...or worked there themselves."

Fire crews described seeing a "scene of devastation" when they arrived.

The building contained heating oil, kerosene, acetylene and asbestos. There is also a silo containing highly flammable wood flour used for making wood laminate flooring.

The fire service added: "Cheshire's search dog Bryn and his handler have started initial work on part of the site with other search dogs en route to the site.

"Specialist equipment is being organised to move two vehicles near the factory which were badly damaged in the fire to improve access to the factory."