A 90-year-old US lottery winner is suing her son and his financial advisers for allegedly mismanaging her fortune.

Gloria Mackenzie became the biggest single Powerball winner in US history when she took home the $278m (£209) windfall six years ago.

But the Florida resident claims the money was put into poor investments, costing her millions of dollars.

Her son, Scott Mackenzie, says the lawsuit is not justified.

Ms Mackenzie was 84 years old when she won $590.5m on the Powerball in 2013. After opting to take the money in a lump sum and deducting taxes, she received $278m.

She says she gave half of her winnings to her son, who had vowed to look after her for the rest of her life.

With no experience in managing large amounts of money, she also gave her son power of attorney over her own finances.

But in a lawsuit filed last month in Jacksonville, Ms Mackenzie claims that low-return investments made by her son and his financial advisers cost her tens of millions of dollars that she could have earned if the money had been better managed.

She was also being charged $2m in fees, according to the suit.

In court papers, Mr Mackenzie says there is no basis for the legal action.

The claims "are based solely on allegations that Scott introduced Gloria to an investment adviser who put her in conservative investment vehicles, in accordance with her chosen investment objectives, and effectively preserved her wealth," he said in court papers.