Investors pouring into gold helped push the total assets of the SPDR Gold Trust to $76.7 billion, making it the largest exchange-traded fund in the world for the first time.

For the first time ever, the gold trust, which owns physical bars of gold kept in vaults, surpassed the $74.4 billion SPDR S&P 500 ETF , which tracks the S&P 500 stock index, as of the market close on Aug. 19, State Street Corp's Global Advisors unit said on Monday.

Bullion surged 6 percent in the last three sessions, up $400 per ounce since July, making it one of this year's best-performing assets, now up 33 percent year to date. The S&P 500 has lost 10 percent so far this year.

On Monday, spot gold rallied nearly 2 percent to a record near $1,900 an ounce while stocks in the S&P 500 Index rose just 0.4 percent.

Interest in gold-backed exchange-traded funds jumped last week. Holdings of State Street's gold ETF recorded an inflow of over 30 tonnes, its biggest one-week rise since mid-July last week. With 1,290.76 tonnes stored as of Friday, the fund is near its highest level of the year.

The S&P 500 ETF had been the largest in the category since it opened in January, 1993 as the first U.S. exchange-traded fund. The fund remains by far the most widely traded ETF, with average daily volume of close to 200 million shares.