The Internal Revenue Service is looking for Hawaii taxpayers who are missing 693 refund checks totaling more than $680,000 that were returned to the IRS by the Postal Service due to mailing address errors.

The average refund is $983, the IRS said in a news release.

If a refund check is returned to IRS as undeliverable, taxpayers can usually update their addresses with the "Where's My Refund?" tool on IRS.gov. Once the IRS receives an updated address it can send out the refund check.

The Web site tool enables taxpayers to check the status of their refunds. A taxpayer must submit his or her Social Security number, filing status and amount of refund shown on their 2008 return. Taxpayers can access a telephone version of "Where's My Refund?" by calling 800-829-1954.