The Waikato DHB has confirmed a cluster of COVID-19 cases in Matamata are linked to a St Patrick's Day celebration.
There are 23 confirmed cases in the area and most have been identified as attending the March 17 event at Redoubt Bar, or were directly linked to those who went.
Ministry of Health Director-General Dr Ashley Bloomfield said on Monday a full investigation has been launched into how that cluster appeared.
"We know there's a cluster in Matamata and we know that there was an index case that was associated with overseas travel," he said.
"What's not clear is the extent of which it might be community transmission, so we're doing a full investigation."
Incident controller for the health response in Waikato Leena Singh said in a statement they are continuing to find close contacts of everyone who went to the event and to discount community transfer.
"With the alert level 4 lockdown now in effect, residents of Matamata can be assured that they are already undertaking the safest possible practice by isolating and should continue to follow the national guidance," she said.
"Please stay in your bubble as this is the most effective way to eliminate the virus."
Singh said any locals with symptoms of COVID-19 should contact Healthline, their GP or go to a Community Based Assessment Centre (CBAC). They should also inform staff if they went to the Redoubt Bar event or if they had close contact with anyone who did.
Any visitors to Matamata who went to the bar for the St Patrick's Day celebration and have symptoms should also contact Healthline and their doctor. Singh said it is important to know whether there has been spread beyond Matamata.
The Waikato DHB is setting up a CBAC at the Matamata Civic Centre which is expected to operate from 3pm on Monday. It will be open there until the end of the week.