UK Prime Minister Boris Johnson hailed her as the nurse who kept him alive. But New Zealander Jenny McGee says she was "just doing her job" as she would for any patient.

Johnson singled out "Jenny from Invercargill" after recovering from coronavirus, saying she was one of two nurses who stood by his bedside for 48 hours "when things could have gone either way".

They were the reason that "in the end, my body did start to get enough oxygen", he said after being discharged from St Thomas's Hospital in central London.

McGee's family in New Zealand were delighted and surprised when Johnson personally thanked her. They knew it was likely she would care for him because she was a senior sister in the intensive care unit.

"But she never really confirmed or denied that she was involved until he was out of hospital," said her father, Mike McGee. "Then he told the world."

Jenny McGee, who has worked at St Thomas's for eight years, spent several of her 12-hour shifts at the Prime Minister's side.

"When you're an intensive care nurse you are nursing one on one with the patient. You are right there all the time, tending to their every need basically, monitoring all the machines," Mike McGee said.

"These people she is dealing with every day are seriously, seriously ill. And it's her job to try and get them well again and get them out of the hospital.

"In that time, obviously they had a chance to talk about things. What else do you do when you're nursing someone for 24 hours?"

Her brother, Rob McGee, who is also living overseas, said: "We are all very proud of Jen, not just in the support she gave Boris but what she has been doing helping everyday people."

Johnson's personal note of thanks brought a flood of international attention to a woman who grew up on a farm at the bottom of the world. When she headed out to her night shift on Monday morning (NZ time), there was a crowd of reporters on the doorstep of her London flat.

Prime Minister Jacinda Ardern said she had sent Jenny a note on Facebook but was yet to hear back.

"All day long the media have been asking about Jenny from Invercargill," her father said.

"But she doesn't crave publicity. She said 'Dad I was just doing my job, I was nursing him just like I was nursing any patient who came through the door'."

McGee grew up in Edendale in Southland and went to to Menzies College in Wyndham and Verdon College in Invercargill. She was not set on nursing at first and "needed a push from her parents" to pick it as a career. She chose to go to the Otago School of Nursing to experience the Dunedin student lifestyle.

Her first job was at Royal Melbourne Hospital and she later moved to St Thomas's and rose up through the ranks to become Senior Sister. Although some New Zealanders have been forced to return home because of stricter visa conditions in the UK, her hospital vouched for her and helped her stay in the country.

When coronavirus arrived in the UK it was clear McGee would be on the frontline.

"There was a worry about how she would protect herself," Mike said. "And she said 'Look, I'll be ok, it's more you oldies back home, make sure you look after yourself'.

"Jenny just seems to have that knack of being able to keep everybody calm and support them and let them know the medical people are doing the very best they can for their loved one."

Johnson listed a number of the frontline staff who cared for him during his week-long stay but singled out McGee and a Portugese nurse, Luis Pitarma, noting that he hoped they wouldn't mind him mentioning them.