On the day that the Dow Jones industrial average lost more than 800 points, over 3%, some Vanguard clients were unable to make any trades.

According to a Vanguard spokeswoman as well as tweets from the company, a “network connectivity issue” was causing difficulty for some clients to access Vanguard “via the web or phone.”

The spokeswoman said the access issues started at 6 am Eastern on Wednesday and were “intermittent and periodic.” Vanguard says it is “working as quickly as we can to restore full access and will provide updates as they become available,” and it apologized for the inconvenience.

For clients experiencing access issues, Vanguard “encourages them to try to log in or call back a few minutes later,” according to the spokeswoman. She did not say how many clients are affected.

— Check out U.S. Stocks Plunge; Dow Off More Than 800 Points on ThinkAdvisor.