A 'small number' of positive Covid-19 cases have been linked to St Sampson's Co-op Grande Marche.
It's as 46 more people have been diagnosed with the infection in the latest 24 hour period.
The number of known active cases in Guernsey has risen to 236. Five people with the virus are in hospital.
Public Health says it has identified some cases linked to the supermarket.
The States of Guernsey says it and the Channel Islands Cooperative Society have 'quickly acted to close the store' on Sunday, deep clean the premises and carry out testing for all staff so the shop can reopen 'as quickly as is safe to do so'.
Customers do not need to self-isolate unless they are contacted by the Contact Tracing Team.
Supermarket staff and ports staff are among 'essential workers' to be tested at the East Arm testing facility.
The States says this is to ensure that these areas are carefully monitored and to give assurance that staff are able to continue working safely.
Targeted testing is going on to support essential services that have been impacted by the number of people asked to self-isolate, for example those who attended the Dance Festival at Beau Sejour, to allow staff to continue working where appropriate.
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