Major U.S. crypto exchange Coinbase Global Inc. launched its NFT marketplace on Wednesday, in a sign of confidence in the niche digital assets, i.e. non-fungible tokens, even as the market shows signs of cooling.

The platform, first announced in October, will initially be available for a "small number" of people in the United States, a Coinbase spokesperson said. More users will be added from a waiting list over the next three to five weeks as the platform is tested.

NFTs are a type of crypto asset which use blockchain to record the ownership of digital files such as an image, video or piece of text.

They exploded in popularity in 2021, echoing the ballooning embrace of crypto such as bitcoin by mainstream investors and companies. Some NFTs have fetched millions of dollars worth of cryptocurrency, but growth has slowed in 2022.

On the popular marketplace OpenSea, NFT sales on the ethereum blockchain halved to around $2.5 billion in March, from $5 billion in January.

"We believe NFTs are here to stay," a Coinbase spokesperson said. "Beyond buying and selling NFTs, our marketplace offers better ways to find the right communities and better spaces in which they can feel connected with each other."

NFTs are largely unregulated, and reports of scams, fakes and market manipulation are common.

One marketplace, LooksRare, has generated billions of dollars worth of volume from a small number of wallets trading NFTs repeatedly back and forth between themselves at inflated prices.

Another marketplace, Cent, halted transactions in February because people were selling NFTs of content which did not belong to them.

Coinbase said it will allow copyrighted or fraudulent content to be reported. The ability to create (or "mint") NFTs will be added to the Coinbase NFT platform in future, the spokesperson said.