Seventy-nine people have been placed in isolation in Jersey after nine new cases of Covid-19 were identified.
The island's government said it had contained the outbreak, although further contact tracing could identify more positive cases.
Investigations have shown the cluster spread after "a number of adults got together in each other's homes".
An event attended by a person who broke mandatory isolation after travelling is being investigated.
Public Health guidelines in Jersey currently advise against visiting other people's homes and require everyone who arrives in the island to isolate until they have received a negative test after 10 days.
Failure to self-isolate on arrival in Jersey is a criminal offence and carries a fine of up to £10,000.
"I want to thank employees across Public Health, Contact Tracing and Enforcement who have prevented a small outbreak from going any further," said Health Minister Richard Renouf.
"This deliberate flouting of public health advice has led to nine people testing positive so far, and 79 people having to isolate.
"We will not be able to continue our reconnection plans if this kind of behaviour becomes more prevalent," he added.
Under current plans, pubs and restaurants in Jersey will be allowed to reopen for table service only from Monday, with up to 10 people allowed in a group, including people from different households.
Ministers are still advising against household mixing because there are "no control measures possible in private homes".