Worries over global growth got part of the blame for a stock-market selloff that gained steam in afternoon trading, taking the Dow Jones Industrial Average DJIA, +1.33% down by more than 400 points and turning major indexes negative for the week. The Dow industrials were down 448 points, or 1.7%, in recent trade at 25,259, leaving the blue-chip gauge down 0.4% for the week. The S&P 500 SPX, +1.59% fell 1.8% to 2,759.02, while continued weakness for tech shares saw the Nasdaq Composite tumble 2.2% to 7,472, leaving it 0.3% lower for the week. A sharp selloff in Chinese equities early Thursday helped set the tone, analysts said, underlining concerns about the global growth outlook, though, much like last week's equity rout, there appeared to be no single catalyst for the weakness.