HONG KONG, March 9 (Reuters) - China's Autohome Inc is set to raise $688 million by pricing its shares at HK$176.3 ($22.71) each in its Hong Kong listing after its U.S. stock dropped by 12.5% on Monday, according to two sources with direct knowledge of the matter.

The online vehicle firm sold 30.29 million shares as part of the transaction.

The sources declined to be identified as the information was not yet made public.

Autohome did not respond to a request for comment.

Autohome's New York-listed American Depository Receipts (ADR) slid by 12.5% on Monday, as part of the rout felt across Wall Street. The stock is down 30.1% from its recent peak on Feb 16.

The price due to be set in Hong Kong is a 5.5% discount to the U.S. closing price on Monday.

Four Hong Kong shares are equal to one of the company's ADRs, according to the deal's terms.

A maximum price of HK$251.8 per share had been flagged when the deal launched last week which would have raised up to $983 million.

Autohome has the option of selling an extra 4.54 million shares as part of a so-called greenshoe option to increase the size of its fundraising. ($1 = 7.7638 Hong Kong dollars) (Editing by Jacqueline Wong)