Government ministers are lambasting a National MP who claimed a homeless man was able to sneak into isolation for two weeks, after the Ministry of Health said it could not stack up the story.

But that MP – National's health spokesman Michael Woodhouse – is sticking by his story, telling the Herald his source was reliable.

"The inability of the Ministry to confirm it doesn't constitute evidence that it didn't occur," he said.

This comes after Director-General of Health Ashley Bloomfield said the Ministry of Health had not been able to verify the story.

"As far as we can tell this cannot be verified and might be an urban myth," Bloomfield said.

NZ First Minister Shane Jones said this afternoon said Woodhouse's claims were a "shallow attempt to spread fear and confusion".

He said it's not up to Woodhouse to stack up "that apocryphal story".

"It's not right to spread any rumour that leads to disunity and fear – certainly when we have all been through a lockdown and we have spent a fortune on keeping the economy going."

In the House, Housing Minister Megan Woods accused Woodhouse of "politicking" over the issue.

Prime Minister Jacinda Ardern also appeared to be critical of Woodhouse – albeit not as much as Jones.

"I do think we should we should make sure that we can verify things before we state them."

She told reporters that the Ministry of Health does take claims seriously and the issue had been looked into.

"We do want to make sure we're putting resource into the things that really matter; so I would rather chase things that we can actually demonstrate have some factual basis to them."

Woodhouse said that the response by Bloomfield was predictable.

"What is irrefutable is that the anecdote was given to me by a reliable source."

Last week, Woodhouse claimed last week a "reliable source" told the National Party the homeless man pretended he was a new arrival completing his 14-day isolation.

"One of the five-star hotels housed a homeless person for a couple of weeks under the pretence that it was someone who came back from overseas," he said.

"When the person was ready for discharge, he was asked for a forwarding address, only to tell the official that he didn't have one - because he was homeless."