Google said on its app status page: "We're aware of a problem with Google Drive affecting a significant subset of users. The affected users are able to access Google Drive, but are seeing error messages and/or other unexpected behaviour."
Users were unable to access their files using the Windows desktop client for Drive but the Web interface was working.
Using the client resulted in an error message, "Sorry, Backup and Sync needs to quit", according to the app status page messages.
"We are deploying an updated client now. The Windows client will automatically update with this fixed version within the next 12 hours."
It added that affected users could also download the updated version of the client from this site, adding that affected Windows 10 users may need to sign in to their Google account within the client.