HSBC customers have been locked out of their online accounts for the second time this month following a cyber-attack that the bank says it "successfully defended" itself against.

A message on HSBC's website today said that online banking was "unavailable" after a "denial of service attack", but that customers could still access their accounts via telephone banking.

Update 5pm Friday: HSBC says "normal services are returning", but some MSE users are still experiencing problems logging on to their accounts.

A statement on the bank's UK Twitter feed posted just before 11.30am said: "HSBC UK internet banking was attacked this morning.

"We successfully defended our systems.

"We are working hard to restore services and normal service is now being resumed. We apologies for any inconvenience."

An update posted at 4.45pm said: "Internet and mobile banking recovering, but we continue to see DDOS attacks. Situation closely monitored, but normal service is returning."

HSBC says that all of its major branches will be open on Saturday. Customers of First Direct, also part of the HSBC group, are not affected.

HSBC customers began reporting problems accessing online banking on social media at around 7am today.

A denial of service attack swamps a website with more traffic than it can handle to attempt to drive it offline.

Earlier this month millions of HSBC customers were unable to access their accounts online for at least two days because of a major "technical issue" rather than an attack.