Oxfordshire County Council and Oxford City Council have temporarily taken their websites offline while examining a known technical problem affecting websites worldwide.
Oxfordshire County Council’s main site, which provides access to parking and traffic filter permits, library accounts, information, care services and community support, is currently unavailable.
Users receive an error alongside a Google warning that attackers could attempt to steal information such as passwords, messages or credit card details.
Oxford City Council has also suspended access to its website.
The site normally enables residents and businesses to pay council tax and business rates, submit planning applications, access housing and bin services, and use leisure facilities.
Visitors are told that the website is temporarily offline and closed for maintenance.
A spokesperson for Oxfordshire County Council confirmed that both websites had been taken down as a precaution.
The authority added that the return date for the county website had not yet been determined and that further updates would follow.
Oxford City Council stated that the disruption was not a cyber incident.
It said the website was unavailable because of a worldwide problem with the underlying technology and confirmed that the council could still be contacted by phone on 01865 249 811.