A 15-year-old heiress to two powerful British dynasties — the Goldsmith and Rothschild families — has died in a quad bike accident on a family farm.

Key points: Iris Goldsmith reportedly became trapped when her vehicle overturned

Iris Goldsmith reportedly became trapped when her vehicle overturned She was remembered on social media as "a lovely, gentle girl"

She was remembered on social media as "a lovely, gentle girl" Her parents are believed to have a joint fortune of over $538.8 million

Iris Annabel Goldsmith, the daughter of millionaire financier Ben Goldsmith and his ex-wife, Kate Rothschild, was killed in an accident on her father's property in Somerset.

"Dear God, please can I have my beautiful, brilliant, kind little girl back," Mr Goldsmith posted on Twitter. "It hurts so much I can't describe."

The BBC reported Iris became trapped when her vehicle overturned and police were not treating the accident as suspicious.

South West Ambulance Service told the BBC an air ambulance was sent to the scene after emergency services were called about 3:00pm on Monday (local time).

Iris's parents married in 2003, uniting two of Britain's most wealthy families.

The couple also had two sons — Frankie, 13, and Isaac,11 — before separating in 2012.

Mr Goldsmith and Ms Rothschild are believed to have a joint fortune of over 300 million pounds ($538.8 million).

Iris was a student at Wycombe Abbey boarding school in Buckinghamshire.

Kate Rothschild and Ben Goldsmith were married in 2003. ( Reuters: Lee Besford )

Tributes posted on social media

Tributes were posted on Twitter and Facebook offering condolences to the family and describing the teenager as "beautiful", "charming" and "an absolute delight".

Jemima Goldsmith — Mr Goldsmith's sister and former wife of retired cricketer and current Pakistan Prime Minister Imran Khan — tweeted an appeal to the media to allow the family to grieve the death of her niece in private.

"We are dealing with a devastating family tragedy," she said.

Loading

Iris's former teacher Alison Holford tweeted she was "heartbroken to hear of the tragic death".

"I will never forget her lovely smile and generous nature," she wrote.

Isabel Goldsmith — Mr Goldsmith's sister and aunt of the dead girl — posted condolences to the family on Facebook.

"Iris was a lovely, gentle girl and Ben is the most loving, caring father," she said.

Who are the Rothschild and Goldsmith families?

The Rothschilds are arguably the most famous banking family in Europe.

The family business began in the 1760s when Mayer Amschel Rothschild started a banking house in Frankfurt which provided banking services to royals and nobles.

He then had five sons, who established branches in London, Paris, Vienna and Naples by the 1820s.

As the family rose to power, the five sons were made barons of the Austrian Empire.

In the late 1800s, members of the family were elevated to the British nobility and, in 1858, Lionel de Rothschild became the first Jew to enter the British Parliament.

Over the centuries, the Rothschild dynasty expanded to mining, energy, real estate and winemaking.

While the exact net worth of the Rothschilds is not known, it has been estimated to be in the hundreds of billions.

Meanwhile, the Goldsmiths are members of another prominent banking family with German roots — the Goldschmidts (the name has since been Anglicised).

In the 1800s the Goldschmidts, along with the Bischoffsheim family, managed Bischoffsheim, Goldschmidt & Cie bank, which eventually merged into multinational banking conglomerate Banque de Credit et de Depot des Pays-Bas.

That merged with Banque de Paris, which has evolved into what is now BNP Paribas, the eighth largest banking group in the world.