The fire chief overseeing the search mission at Didcot power station has said it is "highly unlikely" that the three missing people are still alive.
The Didcot power station collapsed yesterday afternoon, killing one and injuring five others.
Sniffer dogs and search equipment including two drones had been deployed to find the missing people, but after nearly 24 hours, Oxfordshire Fire and Rescue Service chief fire officer David Etheridge has warned that "no signs of life" have been detected.
A major incident was called after the NPower-owned 10-storey building collapsed yesterday afternoon at around 4pm. The building was due to be demolished within the next fortnight.
One person was declared dead at the scene. More than 40 people were treated at the scene for dust inhalation, while five others were taken to hospital. One of the men is said to be in a "serious, but non-life threatening condition".
Assistant chief fire officer Simon Furlong said this morning that so far the teams "haven't picked up any clear signs of life".
Emergency services including Oxfordshire Fire and Rescue Service, South Central Ambulance Service and Thames Valley Police attended with two air ambulances, four specialist Hazardous Area Response Team vehicles and six ambulances.
Furlong added: “The remainder of the building is very unsafe which is hampering search. This is a very difficult situation with a very unstable structure.
"The safety of emergency service personnel has to remain our priority, while recognising how hard this must be for families waiting for news of loved ones overnight. Our sympathies are with them, and the family of the person who died here yesterday.
"An expert from Cheshire with similar experience is due on site today to advise on the search.
"The police will be taking over control of the site as part of ongoing investigation but we are continuing working with fire services from Bucks, Hants and West Midlands, and this work may continue for several days.”
An Npower spokesperson said last night: "We can confirm that shortly after 4pm this afternoon part of the Boiler House at our former Didcot A Power Station site in Oxfordshire collapsed while an external demolition contractor was working in it.
"It is with great sadness that we understand that there has been one fatality, four people have been taken to hospital and three people are currently missing and unaccounted for.
"Our thoughts are with the families of all those involved in this tragedy. We will provide updates as we receive them. We are working with the emergency services who are currently on site to understand the cause of this collapse."