The Nigerian authorities say more than 270 inmates are now known to be missing after escaping from custody when severe flooding damaged a prison in the north-eastern city of Maiduguri.

So far, seven are back in detention.

The flooding was caused by the collapse of a dam following heavy rainfall.

Several hundred thousand people in Maiduguri, which is the Borno state capital, have been forced from their homes by the floodwaters and at least 30 have died.

Borno state Governor Babagana Zulum described the extent of the damage as "beyond human imagination".

This is the first time that the Nigerian authorities have admitted to the numbers who fled custody.

The Nigerian Correctional Service (NCoS) said on Sunday that after the walls of the medium security prison had been damaged, inmates were in the process of being transferred and some managed to escape during the "evacuation to a safe and secure facility".

Governor Zulum had earlier told the BBC that some members of the Islamist militant group Boko Haram were among those who had got out.

But it is not clear how many of the fugitives are linked to jihadist violence.

NCoS spokesperson Umar Abubakar has tried to assure the public that his organisation is working with security agencies to recapture those who fled.

It has published the photos of the missing men and has urged people to remain calm adding that the prison break does not affect public safety.