The babies were born more than three months early
A woman has given birth to sextuplets 14 weeks early at the John Radcliffe Hospital in Oxford.
Vicky Lamb, 31, gave birth to four girls and two boys, ranging in weight from 1lb 5oz (0.6kg) to 1lb 15oz (0.9kg).
Mrs Lamb, of Oxford, who had fertility treatment, is said to be recovering well following the birth on 14 May.
The babies are in intensive care and doctors have said the next few days will be "critical".
Publicist Max Clifford, who is representing the family, said Mrs Lamb became pregnant after taking the same fertility drug she used before the birth of her first child, Gracie, now aged five.
"They are just incredibly grateful for the John Radcliffe Hospital, the doctors and the nurses," he said.
Talking about when Mrs Lamb and her husband Andy, also 31, might be able to take their babies home, Mr Clifford said: "It is a long way off.
"They are fighting for their lives, they are still critical."
The hospital said sextuplets were born once in every 4.5 million pregnancies.
Last year a woman gave birth to six babies at the Royal Jubilee Maternity Hospital in Belfast.
Before that the last surviving sextuplets in the UK were born in 1993, according to the Multiple Births Foundation charity.
The John Radcliffe Hospital said: "Staff... feel privileged to play their part in such an unusual birth.
"A large team of doctors and nurses were present at the delivery or involved with the immediate management of the babies.
"There were several weeks of planning the delivery prior to the birth."
Consultant neonatologist Dr Kenny McCormick said: "Babies that are born this early need a lot of specialist care.
"They are receiving round-the-clock intensive care and specialist nursing at the moment and their condition is constantly monitored."
Keith Reed, chief executive of the Twins and Multiple Births Association, said it was "truly amazing news".
He added: "We waited for decades for the birth of sextuplets in the UK and now two sets have now been born within the space of the year.
"Families in this situation face a rollercoaster of emotions and we all wish the whole Lamb family well."