Earlier, the company said access to accounts and online trading platforms were unavailable.

Officials were not immediately available to explain the cause of the problem nor how long access to its website was unavailable.

Schwab customers used Twitter accounts to express dismay at being unable to place premarket orders.

Stock trading has been heavy in the past week as a result of strong market volatility that active investors seize upon to make trades.

Earlier in the week, discount brokers Scottrade Inc. and TD Ameritrade reported some order processing problems.