Shares of Tata Motors and Ultratech Cement plunged briefly plunged by 10% each in the last half hour of trading on the National Stock Exchange (NSE) on Friday, after a series of shares were sold at lower prices.

The block sales took place in the NSE at much lower prices than either company was trading at the time, sending the shares crashing and sparking speculation of a freak trade.

An NSE official said the falls appeared to have come from a single broker and the exchange was looking into the matter.

The falls were within the exchange's limits, he added.

Tata Motors shares fell 5.5% after six separate block deals comprising a total 2.07 million shares took place at an average price of Rs.275.

The sales sent Tata's shares as low as Rs.268, before recovering to close the day at Rs.293, down 1.7% on the NSE.

Ultratech shares fell 3.4% after one block deal comprising 41,863 shares took place at an average price of Rs.1,854.

Shares fell to Rs.1,712 but closed the day at Rs.1,870, down 1.7% on the NSE.