A convicted attempted murderer is one of two men at large after they broke out of HMP Pentonville, reportedly using diamond-tipped cutting equipment to break through cell bars.
Matthew Baker, 28, was on remand awaiting sentencing after being convicted two weeks ago of stabbing a man during a dispute in Dagenham, the Metropolitan Police said.
The other man who fled the Victorian-built Category B prison in London on Monday was named as James Whitlock, 31, who was also being held on remand after being charged with conspiracy to burgle over 19 alleged ATM thefts.
A Metropolitan Police spokesman warned that the public should not approach the men "as they could become violent".
Pictures of the two men were released by Scotland Yard as the investigation into how they managed to get out of the prison continued.
The pair - understood to be cell mates - are said to have scaled the perimeter wall of the prison.
There were suggestions that the escape was uncovered when staff found the inmates' beds stuffed with pillows in the shape of bodies.
Police launched a manhunt after the escape was reported shortly before noon on Monday.
Following the breakout the head of the prison's independent inspection watchdog said Pentonville was "a soft target" because of the "dilapidated" state of its windows.
Whitlock was described by police on Monday as being white, with a slim build and the word "Tracy" tattooed on his torso. Baker, described as white and ginger-haired, was due to be sentenced on November 11, a Met spokesman added.
It is not known what clothing either man was wearing during the escape.
A woman who visited the prison said an inmate had told her the two prisoners escaped through a cell window on the fifth floor. She said it was rumoured that they used bed sheets to lower themselves down.
The woman, who wished to remain anonymous, said: "They cut one of the bars and then they came down through the window. They are assuming that it was probably bed sheets and it was at night."
A male visitor, who also wished to remain anonymous, said he was told the escapees folded bed sheets in the shape of a body to fool staff into believing they were asleep.
The episode came hours after a major disturbance at another prison, HMP Bedford, and will spark fresh questions about the state of jails in England and Wales.
Camilla Poulton, chairwoman of Pentonville's independent monitoring board, said one of its members had been to the prison on Monday.
Ms Poulton said: "Clearly this is a regrettable incident. As we reported in the summer to the Secretary of State for Justice, HMP Pentonville will remain a soft target for contraband and other security breaches as long as its dilapidated windows are in place, notwithstanding the efforts of management and staff."
HMP Pentonville opened in 1842 and holds more than 1,200 adult men.
The prison was last year singled out by former justice secretary Michael Gove as "the most dramatic example of failure" in the estate.
Inmate Jamal Mahmoud, 21, died after being stabbed at the jail on October 18 in an attack which left two others injured.
In 2012 convicted murderer John Massey spent 48 hours on the run after he escaped from Pentonville by climbing over a wall using a makeshift rope made from bed sheets.
Figures showed that in 2015/16 there were two escapes from prisons, and the number has not exceeded two in any financial year since 2007/08.
A report published by the Ministry of Justice earlier this year said escapes were "rare" and "taken very seriously". None of those who escaped were still at large by the end of April, it added.
A Prison Service spokeswoman said: "We are working closely with the police and are urgently investigating the matter. Two prisoners at HMP Pentonville were found to be missing on Monday 7 November."
Last week Justice Secretary Liz Truss unveiled a package of measures aimed at reforming prisons after a slew of warnings about violence and safety behind bars.
The strategy includes a recruitment drive to add 2,500 new officers to the front line and "no-fly zones" to stop drones dropping drugs and other contraband into prisons.
The incident at HMP Bedford on Sunday had already sparked fresh scrutiny of the prisons system, with the Prison Governors Association renewing calls for a public inquiry.
It said the Government's white paper on prisons will see the introduction of a "much-welcomed shift from the bureaucratic centre back to governors, but it will not recruit staff needed immediately".
The PGA added: "Consequently, what happened at HMP Bedford this weekend may indicate the start of similar disturbances or worse to come - there is, in short, a real risk to the core security function of prisons - keeping prisoners within its walls."