Workers say they will return to work if there is a major incident

About 150 hospital porters and cleaners at the Greater Manchester hospital are involved in the walk-out, which started on Monday.

It is the third time the workers have walked out.

Their union, Unison, said the industrial action will continue to be stepped up unless an agreement is reached with their employer ISS Mediclean.

The union claims there is a two-tier system of pay for the workers at the hospital, with non-ISS Mediclean staff being paid more to do the same work.

Regional officer Tony Ruane said: "This dispute is getting bigger and stronger the longer it goes on.

'Minimum disruption'

"Until ISS Mediclean's highly paid managers leave their plush and no doubt well-cleaned offices and get round the negotiating table this dispute will not be settled."

Bolton Hospitals NHS Trust has said it is "extremely concerned" by the strike.

ISS Mediclean has also pledged to keep disruption at the hospital to a minimum, and during previous walkouts a "near normal" portering service was maintained.

A spokesman said: "We will continue to work closely with the trust to ensure that disruption is kept to a minimum and that patient safety is not compromised. "

The staff have said they will return to work in the event of a major incident.