** Shares of Horizon Robotics 9660.HK fall 6.6% to HK$6.95 lowest since June 2
** Stock set for biggest one-day pct drop since April 7
** Chinese autonomous driving solutions provider plans sale of 681 mln new shares to key shareholder in a share placement, raising about HK$4.67 bln ($595 mln) for business expansion and R&D investments
** New shares will be issued at HK$6.93 apiece, or 6.9% discount to Wednesday close of HK$7.44 each
** Key shareholder will subscribe for new shares on completion of sale of same amount of existing shares at the same price to third-party investors
** Hang Seng Tech Index .HSTECH falls 1.3%, Hang Seng Index .HSI down 0.8%
** YTD, stock up 97.2%
($1 = 7.8488 Hong Kong dollars)
(Reporting by Donny Kwok)
((donny.kwok@thomsonreuters.com))