"While discussions with the Ministry of Commerce of the People's Republic of China (MOFCOM) are proceeding constructively and are advancing, MOFCOM's review is still continuing," Merck said in a statement on Friday.

Shareholders now have until March 14 to tender their stock. The previous offer period would have expired on February 28.

Merck, the world's largest maker of liquid crystals used in TVs and tablet and smartphone screens, agreed in December to buy AZ for $2.6 billion (1.5 billion pounds) to expand its range of specialist chemicals for hi-tech gadgets.

It said on Friday that 64 percent of AZ shares had been tendered. Merck has made its offer contingent on securing at least 95 percent of the share capital.

(Reporting by Harro ten Wolde; editing by Tom Pfeiffer)

Stocks treated in this article : Merck KGaA, AZ Electronic Materials Group