A woman who was killed in London by a falling tree branch is believed to be a New Zealander.

The Daily Mail has reported a 30-year-old woman was killed when a branch fell on her as she walked through Kew Gardens.

Stormy weather has been working its way across most of Britain with many parts being battered by up to 100kmh winds.

The British Environment Agency had issued dozens of flood warnings across the country, and emergency and civil services were working overtime to clean up a number of weather-related incidents.

The Mail reported a witness at Kew Gardens saying he heard a sound "like three or four gunshots".

When the witness turned around, he saw the woman lying face down with an "extremely large" branch in pieces beside her.

The Mail said the woman, who was killed yesterday afternoon (local time), was believed to be a New Zealander who had been living in London for some time.

It was reported another witness, Gary Baker, was walking nearby and saw the branch come "crashing down" from a tree about 20m tall along the footpath in the Botanic Gardens.

"There was a bang and I jumped around at what sounded like three or four gunshots," he said.

"I looked and could see what remained of the branch.

"I didn't see it hit the woman, but it was quite clear she was badly hurt. "Someone shouted, 'call an ambulance' as she lay face down on the ground," he told the Daily Mail.

"The branch was extremely large. It was 12 inches thick at least. It was near her, but not on top of her.

"I helped another man to turn her over, on the instructions of the 999 operator, to give her heart massage... Paramedics arrived but they could not save her."

A spokesman for the Royal Botanic Gardens at Kew said: "We can confirm a tragic accident at Kew Gardens this afternoon when a falling tree branch resulted in a fatality.

"We are currently working with police and next of kin are being informed.

"We cannot comment further at this stage but our deepest sympathy is with family and friends."

Police confirmed they were called to the scene, and the matter was referred to the Health and Safety Executive.

The woman's name has not yet been released.