Llandudno Junction, Llandudno and Penrhyn Bay have reported 35 cases of the Delta variant, Public Health Wales said.
The cluster means Conway county now has the highest seven-day infection rate in Wales, with 18.8 positive cases per 100,000 people.
On Friday, the Welsh government will detail whether easing can take place from Monday.
Should it go ahead, Wales would enter Covid alert Level 1, meaning up to six people can meet in private homes from outside your household bubble and up to 30 people can meet outdoors.
Eluned Morgan, Baroness Morgan of Ely and Welsh Government minister for health and social services, has called the rise of Delta variant cases “very serious”.
The official told BBC Wales: “This is becoming very serious; we need to make sure that we try and nip this in the bud in that particular area and obviously all of this will play into how we assess the situation on Friday.
“I don’t think we’d define it quite yet as community transmission, but it’s on its way to becoming that and that’s why we really need people in the area to co-operate with us…to make sure that we can try and suppress this particular variant.
“The last thing we want to see is this spreading across the whole of Wales.”
Nicola Sturgeon, Scotland’s First Minister, said 13 local authority areas in the country will not see lockdown restrictions ease due to concerns over the Delta variant.
The local authorities, including Edinburgh, East Renfrewshire and Stirling, will remain in Level 2 restrictions rather than move to Level 1.
This means around three million people will remain in strict lockdown measures – despite the vaccine rollout.
Ms Sturgeon said she knew it would be “very disappointing” for the millions of people not moving to Level 1, adding: “Taking a cautious approach now, while more people get fully vaccinated, gives us the best chance of staying on the right track overall.
“I appreciate that today’s decisions will feel like a mixed bag. That reflects the fact we are now in a transition phase.
“The vaccines make the outlook positive, but the new variant means the road ahead is still potentially bumpy – so caution is necessary.”
Meanwhile, Boris Johnson has insisted there is “nothing in the data” to prevent England from ending lockdown restrictions on June 21.
Despite the rise in Delta variant cases, Mr Johnson said the Government “always knew that was going to happen” as rules on indoor mixing are eased.
He added: “I can see nothing in the data at the moment that means we can’t go ahead with step four, or the opening up on June 21, but we’ve got to be so cautious.
“What we need to work out is to what extent the vaccination program has protected enough of us, particularly the elderly and vulnerable, against a new surge, and there I’m afraid the data is just still ambiguous.”
Another 4,330 cases and 12 deaths within 28 days of a positive coronavirus test were recorded yesterday.
In total, the UK has now seen 4,494,699 cases and 127,794 deaths.
Yesterday also saw another 108,507 first doses and 338,565 second doses of coronavirus vaccine administered.
In total now, the UK has seen 39,585,665 first doses and 26,073,284 second doses of vaccine administered, equalling 75.2 percent and 49.5 percent respectively.