(Reuters) -Chinese private equity firm Boyu Capital has emerged as the frontrunner to buy a controlling stake in Starbucks' ( SBUX ) China business in a deal that could value the unit at more than $4 billion, Bloomberg News said on Tuesday.

Boyu stayed on in the bidding process after its final contender Carlyle Group has dropped out, a person with knowledge of the situation told Reuters.

Senior partners of the two firms flew to the United States for final negotiations with the Seattle-based coffee chain operator, said the person and two other people with knowledge of the matter.

Starbucks ( SBUX ) is likely to retain a significant minority stake in the China business after the sale, the sources said, who all sought anonymity as the information was confidential.

"We've had very strong interest from multiple, high-quality partners all of whom share our confidence in the long-term growth potential of Starbucks ( SBUX ) in China," Starbucks ( SBUX ) said in a response to Reuters.

The company is evaluating bids from five bidders, it added but declined further comment.

Boyu did not respond to Reuters requests for comment. Carlyle declined to comment.

Bidders who submitted binding offers, which also included HongShan Group, FountainVest and Primavera Capital Group, valued Starbucks China at around $4 billion, or about 10 times over its core earnings, sources have said.

Primavera declined to comment while HongShan and FountainVest did not immediately respond to a Reuters request for comment.

Starbucks ( SBUX ) CEO Brian Niccol told CNBC this month the expected valuation of the China business would be north of $10 billion, including upfront investment by a potential partner, Starbucks' ( SBUX ) retained stake in the China business, and future royalty payments.

The Bloomberg report said other parties, including internet companies, could join the talks as limited partners to help co-finance a deal.

Starbucks ( SBUX ) is divesting in China as fierce competition from domestic coffee chains has clawed into its market share, by offering cheaper products during an economic slowdown that has changed consumer habits.

The chain has countered such challenges with steps such as lower prices for select non-coffee beverages in China and stepping up the addition of new, localised products.

Comparable-store sales in China rose 2% in the quarter that ended on June 29, following a quarter that showed no growth.

Starbucks ( SBUX ) is set to report earnings for the fourth quarter and the 2025 fiscal year on Oct 29.