A council is investigating an increase in “linked” Covid cases among teenagers which have been traced to social gatherings, including parties.

Denbighshire Council said Public Health Wales and Betsi Cadwaladr University Health Board were helping it monitor and deal with the outbreak.

More information about the numbers of places of learning, “other venues” and pupils affected are expected to be released later.

However the Local Democracy Reporting Service understands secondary schools in Ruthin and Denbigh are among those affected and at least 100 children have so far been told to self-isolate as a precaution.

On Friday Denbighshire Council confirmed it was dealing with 10 “linked cases” – but by Monday evening, that figure had increased to 25.

He said: “The increase in linked cases is connected to a number of gatherings and cases are being identified in a number of settings and venues, including schools.

“It is vital residents do not attend any gatherings which contravene Welsh Government Covid-19 guidelines and remain vigilant at this time.

“Enquiries are still being made and further test results are still pending – and we would like to reassure residents we are working to reduce any further spread.”

North Wales Test, Trace and Protect (TTP) have been working since last week to identify those who attended affected gatherings.

The spokesman reiterated calls for people exhibiting Covid symptoms to book a free test at its mobile testing units based at Caledfryn, Denbigh, Rhyl’s Quay Street car park and Llangollen’s Market Street car park.

He added: “You can now go for a free Covid-19 test if you have a wider range of symptoms.

These include flu-like symptoms, not caused by a known condition, muscle ache or pain, excessive tiredness, persistent headache, runny nose or blocked nose, persistent sneezing, sore throat and/or hoarseness, shortness of breath or wheezing and generally feeling unwell.

“Anyone who develops Covid-19 symptoms should book a PCR test at a test centre immediately and, following a positive result, residents should self-isolate and share all relevant information with TTP tracers and advisors.

“We are also reminding those eligible and not showing symptoms to undertake regular lateral flow tests at home.

“These are free and can be ordered online for home delivery and HWB Dinbych will be operating a Covid Support Hub offering collection of free lateral flow tests from Tuesday, June 15.”