China has said it has suffered its "biggest ever" cyber-attack, causing many websites based in the country to go temporarily offline.
The distributed denial of service (DDoS) attack was said to have targeted servers responsible for sites with a ".cn" domain name.
The country has not speculated on who may be responsible.
DDoS attacks, in which a target is flooded with traffic in an attempt to render it unreachable, are common.
The technique is typically employed by hacktivists looking to disrupt websites from operating correctly.
Notice of the attack was posted on the website of the China Internet Network Information Center (CNNIC).
It said that the DDoS had begun at 02:00 local time on Sunday - before intensifying at 04:00.
The CNNIC apologised to the affected users.
It said it would "enhance the service capabilities" of the network responsible for the affected domains.
China is often accused of being responsible for major attacks on Western countries, particularly the US.
A New York Times investigation claimed that China had targeted their systems over a four-month period - but the Chinese foreign ministry described the accusation as "groundless".