The workers are campaigning for a "decent living wage"

About 150 hospital porters and cleaners at the Greater Manchester hospital are involved in the dispute.

The workers are all members of Unison, which says there is a two-tier system of pay at the hospital.

The action comes after a break down in negotiations with their employer, private firm ISS Mediclean.

Bolton Hospitals NHS Trust said care in certain areas would be reduced at the hospital, adding it was "extremely concerned" by the strike.

ISS Mediclean said it provided a "near normal" portering service during last week's strike, while critical areas - such as intensive care, theatres and patient movements - were not affected.

'Two-tier workforce'

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.

"This still remains our priority."

Unison regional officer Andy Gill said: "This is a classic two-tier workforce problem which leaves many staff under-paid and under-valued."

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

Pay row

The dispute arose after a pay claim was lodged to increase wages to �5 an hour for cleaners and �5.50 for porters.

Cleaning staff are currently employed by ISS Mediclean on �4.47 an hour and porters earn �4.61 an hour.

ISS Mediclean says it offered a 3.23% rise backdated to April, in line with national pay guidelines.