HONG KONG (Reuters) - Hong Kong's Henderson Land Development Co Ltd (>> Henderson Land Development Co., Ltd.) has signed an agreement to sell an office tower for HK$9.95 billion (£938.63 million), a spokeswoman said on Friday, and the buyer is a China-backed firm, according to Hong Kong's Companies Registry.

The Hong Kong developer's spokeswoman said the buyer of the building with a gross floor area of almost 330,000 square feet is Fans Group Ltd, a company registered under a China passport holder according to a Reuters check.

Chinese firms have been expanding aggressively in Hong Kong property, one of the world's most expensive real estate markets, buying both residential land and office buildings.

The deal is the largest in the city since CK Asset (>> CK Asset Holdings Ltd) sold a skyscraper in central business district at a world record price of $5.2 billion late last year. The buyer of that skyscraper was also a China-backed investor.

(Reporting by Joy Leung; Writing by Clare Jim; Editing by Muralikumar Anantharaman)