Some 11 cases of Covid-19 have been confirmed at a managed isolation facility in Christchurch, with another 14 possible cases being investigated.

The Ministry of Health says it is investigating after the cases were detected during routine day three testing.

None involved cases in the community, it says.

The ministry says the positive cases are part of a group who are the only people staying at this facility.

Further details will be reported tomorrow, it says.

Stuff has reported several new cases have been detected at the Sudima Hotel where a number of international fishers are staying.

RNZ reported last week that more than 400 foreign fishers were headed to New Zealand to crew deep sea trawlers after failing to find Kiwis to fill the jobs.

A charter flight from Russia arrived in Christchurch on Friday, where the first 200 crew began managed isolation.

The crew are mostly Russians with others coming from Ukraine. Russia has recorded more than 1.3 million cases of Covid-19 - the fourth-highest number of any country.

Seafood New Zealand chief executive, Jeremy Helson, said all the men were tested before they flew here.

"All of these fishers were Covid tested before they took the charter flight into New Zealand. All crewmen tested negative. This pre-flight test was beyond what the government required," Helson said.

"While we wait to see how many cases there are, the fact that they were all detected in quarantine shows the system is working well."