A federal judge has ordered Google to turn over copies of US private wireless data it captured while taking pictures for its "Street View" mapping service.

The encrypted data will be held under seal and kept as a backup in case any of it is determined to be legally admissible evidence in a class action case filed against the Internet giant in federal court in the state of Oregon.

Google is facing civil suits in Oregon and several other US states demanding millions of dollars in damages over its collection of personal wireless information.

The litigation accuses Google of violating local and federal privacy laws when Street View vehicles out taking pictures for its online mapping service also collected unencrypted data from open wireless networks.

Google has apologized for what it said was the inadvertent gathering of fragments of personal data sent over unsecured Wi-Fi systems.

"Google will retain the source hard drive and the encryption key," District Court Judge Michael Mosman said in an order issued this week and posted online on Thursday.

"Access to the data on the source hard drive retained by Google will be determined in the normal course of discovery."

Discovery is the legal term for the process of gathering evidence to be used in court. The "clone hard drive" will be kept safe in court as a backup, according to the judge's order.

US lawmakers have asked regulators whether the Internet giant had broken the law by capturing personal wireless data and Italian and German authorities are also looking into the matter.

Street View allows users to view panoramic street scenes on Google Maps and "walk" through cities such as New York, Paris or Hong Kong.