The 30-year-old from North Kilworth, Leicestershire collapsed and died while running the final stretch of the 26.2-mile London Marathon course on Sunday.
She had been running the marathon with the aim of raising just £500 but as news of her death spread, tens of thousands of pounds was donated to her Just Giving page - and it kept on coming.
As of Wednesday morning, almost £650,000 had been raised on her page via over 50,000 donations, with the charity-hosting website also agreeing to waive their usual 6.5 per cent fee.
Anne-Marie Huby, managing director of JustGiving, said: "The response to Claire Squires' tragic death on Sunday has been extraordinary.
"Out of respect for Claire's memory, we will be donating our fees back to the Samaritans."
Her parents Paul, 62, and Cilla, 63, are being comforted at home by Claire’s sisters and the family of the 30-year-old hairdresser released a statement talking about their great sorrow at her death.
"We are all devastated. It’s a total shock because she was such a fit girl. We’ve no idea what caused her death," the statement read.
"Claire was a bubbly, beautiful girl. She lived life to the full and was so determined.
"Claire has raised thousands of pounds over the years for charities. She was that sort of person.
The statement went on to say: "On behalf of Claire's family and all those who knew and loved her - we would like to say thank you so much for everyone's support.
"Claire would be so happy and overwhelmed with the incredible support that has been offered by thousands of people from all over the world.
Her sister Nicola, 32, added on her Facebook page: "Please in memory of my beautiful sister go on Claire Squires Just Giving and donate some money something good has got to come out of this.”
Claire's boyfriend of two and a half years, Simon Van Herrewege, 31, of Great Bowden, called Claire "the most incredible girl".
"She was happy-go-lucky and so driven. She had a heart of gold. I love her more than words can say and she will be dearly missed," he said.
"She was running the marathon for the Samaritans, it was a cause close to her heart. Her family have been involved with the charity for a few years.”
One of the reasons Claire was believed to be running for the Samaritans was because they helped her family when her brother Grant died of an overdose back in 2001 aged just 25.
Grant died after becoming depressed following the death of his girlfriend Heidi Richardson in a car accident in which he survived.
Her mother Cilla has also volunteered for the Samaritans for over 24 years.
Tests to establish why Claire collapsed as she neared the finish line are expected to take place over the coming days.
She is the 11th participant to die since the event began in 1981 and the first woman. She died with the finishing line only one bend away, after 25 miles of the marathon.
London Marathon organisers said they hope to award Claire a medal posthumously.
"We will be speaking with Claire's family…and one of the things we will be talking about is awarding her a medal," a spokesperson for the race said.