HONG KONG, July 24 (Reuters) - Chinese clinical trial and research firm Hangzhou Tigermed Consulting will start to raise at least $1 billion in its Hong Kong listing from Monday, according to two sources with direct knowledge of the matter.

The deal is unlikely to have cornerstone investors, one source said, which is unusual for a Hong Kong transaction. The decision was made by the board following meetings with prospective investors over the past week, the source added.

The sources could not be named as the information has not been made publicly available.

A Tigermed spokeswoman declined to comment on the company's Hong Kong listing.

Tigermed, which is already listed in Shenzhen, is the largest clinical research trial provider in mainland China, according to its draft prospectus posted on the Hong Kong Stock Exchange website.

With a target of at least $1 billion, Tigermed will be Asia's most valuable healthcare transaction in 2020, topping WuXi Biologics' $984 million share placement in May, Refinitiv data shows.

The world's largest healthcare IPO so far this year, according to Refinitiv, was SK Biopharmaceuticals' deal in South Korea in June which raised $791 million.

Tigermed's regulatory filings in Hong Kong show it could sell up to 15% of its shares. The company’s Shenzhen share price has increased 66% so far this year, which could push the value of the Hong Kong offering higher.

The Shenzhen listed company has a $12.3 billion market capitalisation, according to Refinitiv.

Cornerstone investors, whose shares are locked up for six months, are common features of Hong Kong IPOs with just two deals since 2017 worth more than $1 billion not to feature them, according to Dealogic.

Topsports raised $1.1 billion in October last year and China Literature raised $1.2 billion 2017, without the cornerstones buying in, the data showed. (Reporting by Scott Murdoch in Hong Kong; Editing by Stephen Coates)