Google has lost information at one of its data centres in Belgium after lightning struck four times in a row.
It affected data storage on several disks and resulted in permanent data loss for a small number of Google Compute Engine (GCE) systems.
The company said it is in the process of improving its systems but that some of the disks are unrecoverable, leading to permanent data loss.
Google said only a very small number of disks remained affected, totalling less than 0.000001% of the space of allocated persistent disks in europe-west1-b.
In an online statement, the company said: "Although automatic auxiliary systems restored power quickly, and the storage systems are designed with battery backup, some recently written data was located on storage systems which were more susceptible to power failure from extended or repeated battery drain."
Google took full responsibility and apologised for the incident.
The company added that it would continue to upgrade hardware to improve data retention and enhance response procedures to minimise the effects of possible future incidents.