The Chief Medical Officer's appealing to people with foreign holidays planned to cancel their flight and hotel bookings.
The National Public Health Emergency Team's noticing a "worrying trend" of Covid-19 cases increasing, and new clusters emerging.
Some last week resulted in the need to test over 20 people as close contacts of individual cases.
No new deaths linked to the virus have been reported - but 24 more cases have been confirmed, bringing the total to 25,462.
