Greek financial woes along with efforts by the Chinese government to increase regulation of margin trading sent the markets tumbling to a sharply lower close with Dow collapsing 279 points to 17,826. Nasdaq plummeted 75 points to 4,931.

On the upside

Summit Materials (NYSE: SUM) will acquire a cement plant and seven cement distribution terminals from Lafarge North America.

Mattel (Nasdaq: MAT) reported a smaller than expected loss for the first quarter.

Bloomberg reported that Teva Pharmaceutical (NYSE: TEVA) was exploring the possibility of purchasing Mylan (Nasdaq: MYL).

On the downside

Shares of ForceField Energy (Nasdaq: FNRG) continued falling.

Profit taking weighed down shares of Solazyme (Nasdaq: SZYM).

Bloomberg reported that the Department of Justice was preparing to block the proposed merger of Comcast (Nasdaq: CMCSA) and Time Warner (NYSE: TWC).

In the broad market, declining issues outpaced advancers by a margin of more than 5 to 1 on the NYSE and by nearly 5 to 1 on Nasdaq. The broader S&P 500 plunged 23 points to 2081. Bitcoin lost $4 to $223.