By Anshuman Daga

SINGAPORE (Reuters) - China's HNA Group and a firm backed by Hong Kong tycoon Li Ka-shing are among suitors advancing to a second round of bidding for CIT Group's <CIT.N> aircraft leasing assets valued at between $3 billion and $4 billion, people familiar with the situation said.

CIT's commercial air unit is one of the world's top 10 lessors with 331 aircraft - an attractive target particularly for Chinese firms whose enthusiasm for the $228 billion global aircraft leasing market has climbed in tandem with rapid growth in Chinese air travel.

The people said HNA is the leading contender for the U.S. lender's assets. Bohai Capital, HNA's leasing arm, has said it is planning to add 300 to 400 planes to the 500-plus it has on order and in service.

Others advancing to the next round include Ping An Insurance <601318.SS>, which has an aircraft leasing arm, and Century Tokyo Leasing <8439.T>, which has joint ventures with CIT, the people said, declining to be identified as they were not authorized to speak to the media.

Li's Accipiter Holdings, is a Dublin-based unit of his flagship company CK Hutchison Holdings <0001.HK> and has partnered with U.S.-based Apollo Aviation Group for its bid.

CK Hutchison, a ports-to-telecoms conglomerate, entered the aircraft leasing business in 2014, seeking to diversify its earnings.

"This fits well with their ambition to build a sizeable global leasing business," said one person with knowledge of the group's strategy.

Representatives for HNA Group, Ping An Insurance and Century Tokyo Leasing declined to comment. CK Hutchison and Apollo Aviation did not respond to Reuters' requests for comment.

A spokesman for CIT noted that in a filing to the Securities and Exchange Commission last week, the company said it was still pursuing a dual track process which would either involve spinning off the business or an outright sale. He declined further comment.

CIT, which has more than 100 customers such as Delta Air Lines <DAL.N>, kicked off the sale process earlier this year inviting bids from more than a dozen entities, sources have said.

The second round of bids is due in August, the people said, adding that a meeting with short-listed suitors would be held in New York in the coming weeks.

(Reporting by Anshuman Daga; Additional reporting by Taiga Uranaka in TOKYO; Editing by Denny Thomas and Edwina Gibbs)