MacKenzie Scott, the ex-wife of Amazon founder Jeff Bezos, has donated more than $4bn (£3bn) to food banks and emergency relief funds in four months.

In a blog post, Ms Scott said she wanted to help Americans who were struggling because of the pandemic.

Ms Scott is the world’s 18th-richest person, having seen her wealth climb $23.6bn this year to $60.7bn.

Much of her fortune comes from Mr Bezos who is the world’s richest man and Amazon’s chief executive.

“This pandemic has been a wrecking ball in the lives of Americans already struggling,” she wrote in a blog post on Tuesday, adding that she had picked more than 380 charities to donate to having considered almost 6,500 organisations.

“Economic losses and health outcomes alike have been worse for women, for people of colour and for people living in poverty. Meanwhile, it has substantially increased the wealth of billionaires.”

Donations were focused on those “operating in communities facing high projected food insecurity, high measures of racial inequity, high local poverty rates, and low access to philanthropic capital.”

Last year she signed the Giving Pledge, promising to give away the majority of her fortune. The Giving Pledge is a commitment by the world’s wealthiest individuals and families to dedicate the majority of their wealth to giving back.

“I have a disproportionate amount of money to share,” she wrote in her pledge.

Charity experts have applauded the amount she has given away and how she has done it. Ms Scott has worked with a team of advisers to research thousands of organisations.

“We leveraged this collective knowledge base in a collaboration that included hundreds of emails and phone interviews, and thousands of pages of data analysis on community needs, programme outcomes, and each non-profit’s capacity to absorb and make effective use of funding,” she wrote.

This year Mr Bezos has also been active with philanthropy, committing $10bn to issues related to climate change.

In November, he announced the first of those grants, handing out nearly $800m to 16 groups. Mr Bezos has seen his net worth increase $70bn this year to reach a fortune of $185bn, according to the Bloomberg Billionaires Index.

During the pandemic there has been a massive rise in online shopping benefitting online retailers such as Amazon. Swiss bank UBS said billionaires had done “extremely well” in the Covid crisis.

This year there has been a relatively high number of mega-donations as celebrities, sports stars and business leaders respond to the Covid-19 pandemic and other causes.

Among the most generous was Twitter co-founder Jack Dorsey who announced in April that he was moving $1bn of his assets into a fund to support pandemic relief efforts and other causes. This represents about a quarter of his $3.9bn net worth.

Bill Gates and his wife Melinda have committed $305m for vaccines, treatment and diagnostic development through their charitable foundation, while Harry Potter author JK Rowling donated £1m to help homeless people and those affected by domestic abuse during the pandemic.

On a different theme, Facebook’s Mark Zuckerberg and his wife Priscilla Chan donated $300m to “protect American elections”. The majority of the money went to the Centre for Tech and Civic Life, a non-profit organisation to recruit poll workers and supply them with personal protective equipment, and to set up drive-through voting.

In June, basketball legend Michael Jordan announced he was donating $100m to Black Lives Matters and social injustice causes over the next decade.