Fears are growing for a suspected burglar who escaped from police by entering a city's sewer system.
Officers were "very concerned" for the man's welfare after he entered part of the Leeds network at around 11.30am on Sunday.
West Yorkshire Police have consulted specialists who have expressed concerns about the dangerous conditions in that part of the sewer system.
An alarm at commercial premises in Mabgate alerted police to a break-in and when officers arrived, they saw two people leaving through the roof.
It was thought one of them then entered the sewerage system via a nearby storm drain.
Specialists from Yorkshire Water and West Yorkshire Fire and Rescue Service were called in and a "detailed systematic search" was carried out, police said. No-one has been found yet.
Superintendent Pat Twiggs, from City & Holbeck Division, said: "We can find no indication of that person having got out of the sewer safely and we are therefore very concerned for them due to the extremely hostile environment in the sewer.
"We are making wide-ranging inquiries to try to identify the individual involved but we would like to hear from anyone who has concerns that someone they know is missing and could be involved in this incident.
"We would also like to hear from anyone who has any information which could help us trace and locate anyone who may have been involved. I would like to reassure them that our primary focus is on ensuring the safety of those involved in this incident and the investigation into the burglary is completely secondary at this stage.
"I would hate to think that someone could be sitting on information which could help us to resolve this situation regardless of where they feel their loyalties lie."