The Norwegian sovereign wealth fund, the largest in the world, has officially hit $1 trillion.

Norges Bank, who manages the fund for Norway, said on its website that the rainy-day pot was never expected to grow so large.

"I don't think anyone expected the fund to ever reach 1 trillion dollars when the first transfer of oil revenue was made in May 1996. Reaching 1 trillion dollars is a milestone, and the growth in the fund's market value has been stunning", said Yngve Slyngstad, chief executive officer at Norges Bank Investment Management.

The fund's administrators said that on Tuesday 19 September 2017 at 2:01 a.m. local time, the fund value hit $1,000,000,000,000, or $1 trillion, for the first time.

The bank said a strengthening of the world's major currencies against the U.S. dollar combined with strong equity markets during 2017 had rapidly increased the U.S. dollar value of the pooled capital.

Norway's fund was set up more than 20 years ago to invest revenue arising from oil extraction.

In August, Norges Bank said Nestle, China's Tencent and Swiss company Novartis made the biggest positive contributions to the fund's growth across the second quarter.

In January 2016, the Norwegian government made the first ever withdrawal from the pot of cash to address a slowing economy.