Events planned for today have been cancelled and islanders are being told to practise social distancing again.
In a statement, the States of Guernsey said: 'There is concern that it is not immediately clear how these four individuals contracted the virus, as none are directly from travel or the contacts of known cases or travellers.
'Contact tracing is continuing to determine whether there is a link between the cases and whether these cases are linked or this is as a result of wider community seeding.
'The Director of Public Health is advising all those who were intending to hold gatherings and events of any kind to cancel them.
'Beau Sejour, which was due to host the Dance Festival and other events today, is being closed to the public with immediate effect.'
Care homes and the hospital are being instructed not to allow any visitors and all Islanders are advised to adopt social-distancing measures.
Supermarkets are being told to reintroduce social distancing as quickly as possible.
The States of Guernsey added: 'The Civil Contingencies Authority is meeting today and Public Health are providing updates throughout the day to inform their decision-making.
'The advice to cancel events being held today is at this stage a precaution, however the Director of Public Health and the CCA do not want to see any unnecessary risks taken and would urge all Islanders to take this advice very seriously.'
Guernsey has taken a tough approach to tackling the virus and was Covid-free for many months last year. In recent months it has consistently had fewer that ten active cases. There were six active cases as of yesterday.