Morgan Stanley, one of the world's biggest wealth managers, said its online trading portal for wealthy clients went down on Wednesday.

The bank's message for clients was to call a human adviser to place trades, rather than using the company's website. The issue stemmed from a bug in software from a third-party vendor and not high trade volumes or staff working remotely, according to a person briefed on Morgan Stanley's situation.

Retail brokerages have suffered sporadic outages this month amid unprecedented volatility and volume in markets amid the coronavirus crisis. Most notably, free-trading pioneer Robinhood was overwhelmed by traffic on several days, including one of the biggest days for gains on the Dow Jones.