Blue Sky Power, page-69

It does not seem to be a BSP specific issue:

2016-07-28 15:56:50
Several penny stocks were suspected to be under hefty selling after 3:00 p.m.. BLUE SKY PWR (06828.HK), C ZENITH CHEM (00362.HK), KINGBO STRIKE (01421.HK) and TECH PRO (03823.HK) universally plunged to hit the trough of $0.295, $0.08, $0.26 and $0.2 to $0.37, $0.112, $0.56 and $0.315, collapsing 41%-86%, on volume shooting up to 230 million shares, 100 million shares, 189 million shares and 612 million shares.

http://www.aastocks.com/en/mobile/News.aspx?NewsID=RUM.160728_155650&NewsType=&NewsSource=HK6

Still doesn't give a reason.  Possibly related to "Tech Pro"

http://www.aastocks.com/en/mobile/News.aspx?NewsID=NOW.747701&NewsType=&NewsSource=HK6