An Invercargill woman believes she has foreign accent syndrome - a rare disorder which has gradually changed her New Zealand accent to a British one.

Bronwyn Fox suffers from multiple sclerosis and woke up one morning about two years ago and couldn't see, the Southland Times reported.

A subsequent MRI showed two lesions on the back of her brain.

Mrs Fox said she spoke with a New Zealand accent until two years ago. It had now become standard for her to speak in her new accent.

"My sister who lives in Hamilton, I rang her and I was talking to her... and she didn't know it was me, and when my best friend rang from Christchurch she hung up," Mrs Fox said.

Foreign accent syndrome is believed to be caused by damage to the part of the brain that controls speech. Between 1941 and 2009 there had been 60 recorded cases of the syndrome, which could lead to any alien accent.

Other known cases of the disorder include an English woman speaking with a French accent after having a stroke, and a Norwegian woman who began speaking with a German accent after being hit by shrapnel in 1941.