ISLAMABAD, Pakistan (CNN) - Falling stock prices sparked rock throwing by hundreds of small investors outside the Karachi stock exchange Thursday, prompting officials to call in Pakistan's paramilitary Rangers to keep protestors from storming the building, police said.

Another protest by small investors was also under way outside the Lahore Stock Exchange and police were called there to control the crowd. Protesters were burning tires at the Lahore exchange.

No one was hurt in Karachi but six people were arrested in the melee, which brokers blamed on a 25-percent drop in recent days in the Karachi Stock Exchange 100 Index.

Broker Usman Khawja said the stock index began falling last week after peaking above a record level of 10,000.

The small investors accused big investors of manipulating the stock market and they have called for government intervention.

The Karachi exchange's directors called an emergency meeting Thursday to discuss the crisis.

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