US stocks tumbles as trade war escalates.

Wall Street tumbled on Friday after the US-China trade war escalated in dramatic fashion, with President Donald Trump demanding that American companies seek alternatives to doing business with China after Beijing announced its own slate of retaliatory measures.

All three major US stock indexes ended the session sharply lower, posting their fourth consecutive weekly declines.

The latest exchanges in the long-running tariff row triggered a broad-based sell-off that hit shares of companies with high exposure to China the hardest, such as chipmakers...