A St Patrick's Day event at Redoubt Bar is the focus, but some spread may have happened on days around it as well, Waikato DHB said.

Matamata's coronavirus cluster now has 45 confirmed cases, and more are expected.

All cases were linked - directly or indirectly - to the Redoubt Bar, Waikato DHB chief executive Dr Kevin Snee said in a statement.

"While the focal point remains the St Patrick's Day celebration at the bar, it appears there was also some transmission at that site during the surrounding days as well."

CHRISTEL YARDLEY/STUFF About 200 people had been through the Matamata testing centre since it was set up on Monday afternoon.

Cases to emerge include a man who was at the party, and a teenager who appears to have been infected at the bar days after it.

The number of cases is expected to "shift" again as more people are assessed and contract tracing work progresses, Snee said.

About 200 people had been through the Matamata testing centre since it was set up on Monday afternoon.

Some Matamata residents may be concerned by the number of cases, Snee said, but staying in their "bubble" was the best protection.

Anyone who experiences symptoms should immediately self-isolate from others in their bubble, contact Healthline or their GP and visit their nearest community-based assessment centre CBAC.

CHRISTEL YARDLEY/STUFF Case numbers in the cluster are expected to rise again as more people are assessed and contract tracing work progresses, Waikato DHB chief executive Kevin Snee said.

If they were at the Redoubt Bar during the previous two weeks, or had close contact with someone who had, they should tell staffers.

Anyone who visited Matamata in the past fortnight and who had developed symptoms should do the same.