The Labour Party says there has been a “sophisticated and large-scale cyber-attack” on its digital platforms.
A Labour spokeswoman said the attack had “failed” because of the party’s “robust security systems” and they were confident that no data breach occurred.
It has been reported to the National Cyber Security Centre, she said.
Security procedures had “slowed down” some election campaign activities, she added, but they were now “back up to full speed”.
The party has not specified which of its platforms were targeted, but its main website, Facebook and Twitter accounts are functioning.
The Labour Party spokeswoman said: “We have experienced a sophisticated and large-scale cyber-attack on Labour digital platforms.
“We took swift action and these attempts failed due to our robust security systems. The integrity of all our platforms was maintained and we are confident that no data breach occurred.”
She added that Labour was “out campaigning hard both on and offline for a Labour government that will bring the real change our country needs”.
Voters are due to go to the polls on 12 December.