An investigation has been launched after more than 70 people fell ill following a graduation ceremony event held by the Royal College of Art in London.
Public Health England (PHE) said it is trying to discover the cause of a multiple number of cases of gastrointestinal illness that have been reported.
While PHE said it has received more than 70 reports, the Royal College of Art said the number of cases reported was approximately 200.
The exact location of where the event took place has not been revealed, although it has been confirmed that CH&Co was the caterer at the event.
A spokesperson for CH&Co said: "We are aware that Public Health England and Westminster City Council are carrying out investigations into an incident at the RCA and we are actively assisting them in their enquiries in order for them to bring the investigations to a swift conclusion. Whilst these investigations are taking place, it would be inappropriate to provide further information at this stage."
Dr Deborah Turbitt, deputy director of PHE London, added: "PHE is looking into this case as a matter of urgency. People feeling unwell should isolate themselves as far as possible, and wash their hands when handling food or using the toilet in order to prevent the spread of infection. Those with diarrhoea or vomiting should take care to drink plenty of fluids to stay hydrated."
Richard Benson, chief operating officer at the Royal College of Art, added: "We have received reports from approximately 200 students, guests and staff who suffered gastrointestinal illness over the weekend following the college buffet reception on Friday 29 June.
"This was clearly very unfortunate, and for some of the students and their families was a really unpleasant end to what should have been a day of celebration at the end of the academic year.
"Immediately it became apparent on Sunday 1 July that a number of cases of illness were being reported, the college sought advice from Public Health England (PHE) who have already started an investigation. All students and staff were contacted with advice and support, and have subsequently received regular updates.
"We closed all catering outlets at our Battersea, Kensington and White City sites with immediate effect. The college is continuing to work closely with PHE, our external catering company and other agencies."