A woman has died hours after giving birth to quadruplets at a US hospital.

Erica Morales, 36, never got to hold her babies before she died after undergoing a Caesarian section at Banner Good Samaritan Medical Centre in Phoenix, Arizona.

"They were transporting her from the surgery to whatever room, and she was still unconscious at that point. So, no, she never got to see them," Mrs Morales' best friend Nicole Todman said.

Estate agent Mrs Morales was about seven months into her pregnancy when she delivered three girls and a boy. Ms Todman, one of the few able to visit the babies and said they are doing well.

"They're beautiful," she said. "They have tubes in their mouths and their noses. They've got little monitors and wires all over their body."

The babies will probably remain in hospital for the next two months while doctors help them get stronger and reach a goal weight of 5lbs. Currently, they weigh between just over 2lbs to just above 3lbs.

Mrs Morales was initially admitted to hospital for high blood pressure and complications ensued before she was taken into the operating theatre, Ms Todman said. She does not know what led to her death.

"I don't even care to know," Todman said. "It doesn't matter why. She's still gone."

Hospital spokeswoman Toni Eberhardt released a statement from the hospital saying: "Our heartfelt thoughts and condolences are with the family during this very difficult time."

Mrs Morales and her husband Carlos, who works in manufacturing, had been trying for a baby for two years, Ms Todman said. She said Mrs Morales tried everything from acupuncture to fertility treatments and suffered a miscarriage before becoming pregnant last June.

Ms Todman, who has been best friends with Mrs Morales since childhood, said Mrs Morales was more nervous about being a new mother than raising four children at once.

Because of her previous miscarriage she was apprehensive about getting too excited about the babies' arrival and mainly focused on doing things correctly throughout her pregnancy such as eating enough, Ms Todman said.

"Her focus of her pregnancy was to make sure she did everything to make sure they were healthy so she was able to bring them into this world - and she did," Ms Todman said.

Ms Todman started a GoFundMe fund-raising website for Mr Morales and the infants on Friday. It has already received more than $15,000 in donations.