A crisis-hit prison has been locked down for a “pre-planned intelligence-led search”, authorities said.

Inmates at HMP Birmingham are understood to be confined to their cells as officers conduct sweeps of the jail.

“The search is one part of our long-term safety and security strategy to improve conditions at the prison,” the Ministry of Justice (MoJ) said on Thursday.

It is unclear when the lockdown began at the prison, which is being run by the state after plunging into crisis under private management.

HMP Birmingham
HMP Birmingham is now being run by the Government (Ben Birchall/PA)

A Prison Service spokesman said: “HMP Birmingham has been temporarily placed in lockdown to assist with a pre-planned intelligence-led search of the facility.”

In 2016, a major 15-hour riot gripped the Victorian-era category B jail, with more than 500 prisoners let out of their cells.

HMP Birmingham disturbance
Riot police outside HMP Birmingham during the disturbance in December 2016 (Joe Giddens/PA)

Hundreds of specially trained “Tornado Team” officers were drafted in to bring the disorder, which caused more than £6 million of damage, under control.

It was the worst disorder at a UK jail since the Manchester Strangeways riots in 1990.

HMP Birmingham, which held just under 1,000 inmates at the end of January, will be run by the state for at least another six months after it took over from G4S in August.

HMP Birmingham disturbance
Employees clear debris after the 2016 riot (Jason Alden/G4S/PA)

Chief Inspector of Prisons Peter Clarke published a devastating assessment of the prison last year.

His report, which detailed findings prior to the step-in, revealed inmates walked around “like zombies” while high on drugs in scenes likened to a war zone.

Prisoners flouted rules without challenge from staff, many of whom were “anxious and fearful” as they went about their duties, the assessment found.

It said there had been more assaults at the establishment than at any other local prison in the previous 12 months, control was “tenuous” and many cells were dirty, cramped and overcrowded.