Several hospital wards had to be closed over the weekend after an outbreak of winter vomiting virus.
Visitors reported being unable to see patients at Hillingdon Hospital, Pield Heath Road, Hillingdon, as restrictions were imposed when the Norovirus bug took hold.
One visitor at the hospital who asked to remain anonymous, said: "I was visiting a friend in the Churchill Ward on Sunday and there were three people outside stopping us going in.
"There were no visitors allowed in and there was a porter checking and delivering food we brought in to the patients.
"There were lots of people vomiting and with diarrhoea."
The hospital trust confirmed the outbreak and advised people suffering from symptoms of Norovirus to stay at home.
The Hillingdon Hospital Trust said: "The Trust has been affected by a number of cases of diarrhoea and vomiting that may be attributed to Norovirus.
"This has meant stringent attention to policy and procedures around ward activities and the temporary closure of some of our wards.
"Norovirus is common at this time of year, therefore, to restrict cases of Norovirus being brought into the hospitals from the community, we are advising the public not to visit unless it is essential."