Updated 8.20pm

Massachusetts lottery officials have identified a 53-year-old health care worker who lives in Chicopee as the winner of more than $750 million in a Powerball drawing, the largest prize for a single ticket-holder in the contest's history.

The woman, Mavis Wanczyk, appeared at an afternoon news conference to claim her prize.

"I wanted to get this over and done with, and then everyone would leave me alone," Wanczyk, the mother of a 31-year-old daughter and a 26-year-old son, told reporters. She said she had worked for the past 32 years at a Springfield hospital, but added: "I've called them and told them I will not be coming back."

Wanczyk said she learned of her win when a colleague encouraged her to check her ticket as she left work on Wednesday.

"I said: 'I know it's never going to be me; it's just a pipe dream,'" Wanczyk said, adding that she was shocked to find "I am a winner."

The winning ticket was sold at a Pride convenience store in Chicopee, which is located about 145 km west of Boston, according to the Massachusetts State Lottery. The owner of that store plans to donate to charity the $50,000 prize he will receive for selling the winning ticket, the commission's executive director, Michael Sweeney, told reporters.

Wanczyk will have a choice of receiving annual payments totaling $758.7 million over 29 years, or a lump sum of more than $440 million, before taxes.

Beyond retiring early, she did not say how she planned to spend her winnings.

The odds of a ticket having all six winning numbers are 292.2 million to 1, according to the Multi-State Lottery Association.