An invasive spider with a nasty bite is spreading its population across New Zealand - prompting warnings from experts.

The noble false widow spider has been spotted in Christchurch, Nelson, Northland and Waikato.

Massey University evolutionary ecology professor, Steven Trewick, says their bite is unlikely to kill you - but it's harmful if left untreated.

"Like most spiders, they're not going to bite you because they're not interested in you...but they do have some toxins that are similar to the toxins black widows and redbacks have."

LISTEN ABOVE