New York ? Wall Street finished a turbulent week with another huge drop Friday after major banks warned of further losses on their debt portfolios, raising investor concerns that the credit market slump shows no sign of abating.

The Dow Jones industrial average fell more than 220 points.

Bank of America Corp., JPMorgan Chase & Co. and Wachovia Corp. all said the ongoing credit crisis would cause another round of heavy losses during the fourth quarter. Financial institutions took big hits during the last quarter as losses from subprime mortgages hurt their balance sheets, and these three companies were just the latest to report bad news that sent stocks lower.

BofA said that continued “market dislocations,” including those related to securities it owns that are backed by loans, would affect its fourth-quarter results. The bank did not provide an estimate of how large the impact would be. JPMorgan said difficult conditions may cause a fourth-quarter writedown, but did not say how much.

Wachovia, the nation’s fourth-largest bank, said it faced a $1.1 billion writedown for October alone. Investors also were rattled by speculation that Barclays PLC was about to announce a $10 billion writedown, though the U.K. bank denied the rumors.

“The extent of the situation is unknown, and that uncertainty doesn’t give investors any reasons to believe that a bottom might be in place,” said Todd Salamone, director of trading and vice president of research at Schaeffer’s Investment Research. “We just got more of the same this week rattling investors, and the question for investors becomes what’s the next catalyst to drive stocks higher.”