South Yorkshire Police have confirmed that five bodies were recovered from outside the carriages at the Selby crash scene.
Officers are now focusing on recovering bodies from inside for the first time.
A team of 50 specially trained recovery officers - from the Metropolitan Police, British Transport Police and Greater Manchester Police - will carry out the operation.
Police Chief Inspector Martin Hemingway who is leading the operation to recover the bodies said: "This is a grim task. We appreciate that families of the bereaved are traumatised and we will do our utmost to ensure that bodies are recovered with care and sympathy.
"The officers who volunteer to do this kind of work do it because they know how important it is for families to know their loved ones have been located and have been treated with respect."
He said: "This is going to be quite dangerous work because of the condition of the carriages."
The recovery work is expected to continue for up to two days.
PA