The National Party has apologised after information about people who signed up for two of its petitions was used to solicit donations.

Some signers were left irked when they began receiving emails asking them to donate to the party after signing petitions to save the Lumsden Maternity Centre and an Auckland-to-Kapiti flight route.

The petitions - started by two National MPs - drew thousands of signatures, the former alone collecting more than 2400 last week.

In a statement, a National spokesman doesn't specify how many people had been affected but says a "small error" meant signatories were accidentally added the party's main distribution list.

"We have since gone back to each individual concerned, apologised for the error, and removed them from the main email list," he said.

"This was the result of human error when building the petition. The process for doing so has now been fixed to ensure it won't happen again."

Joanne Dacombe, one of the signers, told RNZ she would be hesitant to sign petitions by the party in future.

"I think they were just a bit opportunist and thought: 'That's it, we'll tap into this'," she said.

In 2016, the Labour Party gathered more than 50,000 email addresses with a Facebook widget that told those signing up what number baby they were born in the public health system.