Westpac New Zealand are apologising for an error, which caused online banking customers to receive a Westpac One notification from "123456789012345678901234567890" with the message "123456789012345678901234567890123456789" between 4 and 4.30pm on Thursday.
In a Facebook post, Westpac said customers had received a string of numbers instead of a message, which had been published to its Westpac One messaging service.
One person RNZ spoke to said they were also unable to login to their account.
However, all services were operational, according to the Westpac status page, and no incidents had been reported by 5pm.
There have been more than 1000 reports of Westpac outages across New Zealand, according to Downdetector, a site which monitors internet outages.
Westpac said the slowness was due to all recipients trying to log in and read the notification at once.