A telco outage is causing headaches at Covid-19 vaccination centres, with those waiting for the jab having to fill out forms manually.

That's slowing the vaccination process, the Ministry of Health said.

"Vodafone has informed the ministry of a nationwide outage which is affecting the digital services at some Covid-19 vaccination centres around the country," the ministry said in its 1pm Covid-19 update press release.

"This means people queuing are having to fill out forms manually, which is adding some time to the process.

"We wish to thank those currently at the vaccination centre for their patience as Vodafone works through this issue."

They were aware of an issue causing intermittent loss of data for some customers on fixed and mobile connections, and were investigating, Vodafone tweeted at 12.14pm.

A Vodafone customer told the Herald they hadn't had access to data since about 9am today.