Belfast City Hospital had to close a cancer ward to new patients last night because of a bug.
It is understood the norovirus, which causes severe vomiting and diarrhoea, was found in one patient resulting in the closure of ward three at the hospital.
Signs were placed in the elevators advising people to wash their hands and visitors were being told to stay away. However, last night a spokesman from the Belfast Trust told the Belfast Telegraph that people were not being told to refrain from visiting, just to "take precautions" on visits.
He also emphasised that the ward was not closed, just that it was not accepting new patients.
It is the second time the bug has forced the closure of wards on the hospital this year.
Belfast City Hospital was also hit in January during the national outbreak of the virus, which saw two wards closed to admissions and at least 20 patients fell ill.
Last night Alliance Health spokesperson Kieran McCarthy said he was shocked the cancer ward was closed to new patients saying there was now more mounting pressure on Health Minister Michael McGimpsey to demonstrate that his strategy to combat hospital bugs is actually working.
"This is an extremely worrying development," the MLA said.
"The Minister has a duty to maintain public confidence in our hospitals. He still needs to convince the public that he is able to deal with this issue decisively and effectively.
"This is not the first time this hospital has been hit by an outbreak and the Minister needs to demonstrate how he will prevent incidents like this in future.
"Healthcare staff at the City Hospital do an excellent job but they must be given the assistance they need to maintain hygiene at the site. It is the Minister's responsibility to ensure that adequate resources are available to address this issue."