April 23 (Reuters) - Assets invested in actively managed U.S. exchange traded funds soared 15% to $611 billion in the first quarter, Morningstar said in a report published on Tuesday, but the vast majority of that money flowed into funds managed by a handful of issuers.

A team of Morningstar analysts headed by Bryan Armour and Ryan Jackson described the market as "lopsided" and calculated the top 10 issuers of active ETFs controlled 74% of assets.

The remaining 310 firms that also have rolled out actively managed ETFs have done so with comparatively "limited success," the analysts said.

"I would have anticipated more breadth and depth" among market leaders, given the overall growth in active ETFs, Armour said in an interview ahead of the report's publication.

When the U.S. Securities and Exchange Commission approved a rule change making the launch of active ETFs as simple as index-based products five years ago, the category represented only 2% of roughly $4 trillion in U.S. ETF assets.

While the size of the market has since doubled to just north of $8 trillion, active ETFs now represent 8.5% of those assets, Morningstar noted, up from 7% at this point last year.

The biggest winners tend to be large asset managers that are relatively new entrants to ETFs, the Morningstar report found. That list includes JP Morgan, Dimensional Fund Advisors and Capital Group, all of which have parlayed strong mutual fund track records into above-average growth in ETF market share.

The JPMorgan Equity Premium Income ETF has been one of the most successful ETFs ever, attracting more than $33 billion in inflows since its May 2020 launch, according to data from VettaFi.

"Issuers that have been aggressive in cutting fees or offering low-fee active ETFs have also won market share," Armour said.

Despite the success of the larger asset managers, new entrants are continuing to join the ETF market.

"We’re still in the very early days for active ETFs," said Matt Kaufman, head of ETFs at Calamos Investments, an established asset manager that launched its first ETFs in 2023. (Reporting by Suzanne McGee; Editing by Jamie Freed)