National Party MP Jo Hayes has apologised for sending a "vile" tweet to a member of the public.

A late Friday night tweet that appeared on an account belonging to Hayes, a list MP based in Christchurch, attacked another user of the site who'd posted a picture from his graduation.

"OMG Youre such a nasty person and i hope that people checking you out for future work will visit your twitter page and see how ugly you really are [sic]," Hayes told Jeremy Greenbrook-Held, seemingly unprompted, just before 11pm.

The target of the vitriol had tweeted about completing his studies after seven years, which he began after struggling to find a new job. The tweet was five months old.

There was initially confusion as to whether the account the tweet was sent from was real, with other Twitter users finding a second account that also appeared to belong to Hayes.

But she's confirmed to Newshub it was real.

"I should not have sent this tweet," the MP, ranked 36th on the National list at the 2017 election, said. "I will delete it and I'm sorry for any offence caused."