The website for Greater Manchester Police has been targeted by an internet hacker in Lithuania.
The force's official website went down at approximately 8pm on Wednesday with users being unable to access the page.
Officers said that initial checks did not reveal anything untoward and the system was quickly brought back online.
A tweet from the GM Police Twitter account read "Few technical issues with http://www.gmp.police.uk over the last 20 minutes" before saying it was "back up and running".
However a short time later the site went down again with a Twitter user from Lithuania claiming responsibility for causing the website to crash.
The tweet using the handle @n0w1337, responded to the force, saying: "I think these problems responsible was me :)" before saying "@gmpolice Again I will leave this site offline".
The Manchester Evening News said the hacker had insisted it was "to show the failure of security in these large systems".
The Manchester Airport website has since also been down with a further tweet from the same account reading: "Official website for Manchester Airport #Offline http://www.manchesterairport.co.uk by @n0w1337 & @g0d1337"
Deputy Chief Constable Ian Hopkins from Greater Manchester Police said: "We are treating this as a denial of service attack, which is a malicious attempt to disrupt services.
"I want to reassure people that the server for the website is not connected to any other force system and that the information contained on the website is all public information.
"We apologise for any inconvenience this may have caused to members of the public and we are working to resolve this issue as quickly as possible."
The attack is being described by officers as a Distributed Denial Of Service (DDOS), which involves many computers accessing the GMP's website in order to overload it.