The main BBC website and the news page are now back online after crashing earlier but the iPlayer service is still down, the broadcaster said.
A spokesman said staff were working to get all pages up and running as soon as possible.
Earlier, when trying to access the bbc.co.uk website, an error message and holding screen appeared.
A message on the screen said: "We are experiencing abnormal traffic to our network or the service or servers it is on is not currently available."
The BBC Press team had tweeted: "We are aware that our website is experiencing some difficulties and we are investigating."
One tweeter, Graeme Cowie (@woodstockjag), said: "BBC website's down. Proof if any were needed that the public funding model doesn't work".
Another, Alexander Bell (@alexbell_), tweeted: "BBC website...offline...need...banal and irrelevant...magazine features...#endofdays".
Normal service has now resumed on most areas of the BBC website.
A spokeswoman said: "Due to a major technical issue, BBC Online was temporarily down on Wednesday evening. Service was restored to most users within an hour. We are working on full restoration as quickly as possible, and are investigating the causes of the outage."