US billionaire Warren Buffett, who has pledged to give away 99 percent of his wealth, has donated 1.93 billion dollars in shares of his company to five charitable groups, financial filings showed.

In notifications to the US Securities and Exchange Commission, Buffet documented donations to five charitable organizations, including a gift worth 1.6 billion dollars to the Bill and Melinda Gates Foundation.

Buffett, who heads investment firm Berkshire Hathaway, pledged in 2006 to donate a portion of 10 billion shares in his company every July to the charity run by former Microsoft chief Bill Gates.

His donation to the organization this year totals some 20.4 million shares in Berkshire Hathaway. The gift is worth around 1.6 billion dollars at the 78.81-dollar-a-share value of company's stock on Thursday, when the SEC notification was filed.

He also informed the SEC of donations of some 713,000 shares each to the Sherwood Foundation, the Howard G. Buffett Foundation and the NoVo Foundation, and a gift of over two million shares to the Susan Thompson Buffett Foundation.

Buffett has publicly called on the wealthy to donate more to charity, and last month urged rich Americans to give at least half of their assets to charity in a commentary co-authored with Bill Gates.

The so-called Oracle of Omaha, whose personal wealth was estimated at 47 billion dollars in 2010, personally pledged that "more than 99 percent of my wealth will go to philanthropy during my lifetime or at my death."

Buffett is known for being an unusual billionaire.

For years, the most successful value investor in history has been complaining for years that his taxes are too low. During a fundraiser for Hillary Clinton in 2007, he said that he was taxed at only 17.7% last year on his $46 million in income, while his secretary paid 30% of her $60,000.

"The taxation system has tilted toward the rich and away from the middle class in the last 10 years," Buffett recently said. Buffett said he did an informal survey of federal taxes paid by his own office staff, and the average was 32.9%, compared to his 17.7%.

"There wasn't anybody in the office, from the receptionists on, that paid as low a tax rate," Buffett claimed.

With earlier reporting by David Edwards and Muriel Kane.