Viewers watching BBC Wales Today on Friday evening were left confused after they were shown the news from Northern Ireland instead.
The change of programme was because of a "major power failure" at BBC Wales' headquarters in Llandaff , Cardiff .
BBC Wales apologised for the disruption and said they were working to restore services as soon as possible.
It tweeted: "We apologise for disruption to BBC Wales services following a major power failure at our Llandaff HQ.
"We are working to restore services as soon as possible."
Those watching BBC Wales Today at 6.30pm were welcomed by the BBC Newsline presenter in Northern Ireland.
He said: "Before we go any further, we need to quickly mention that viewers in Wales have joined us.
"They are not getting Wales Today at the moment due to technical difficulties.
"Our colleagues in Wales are working hard to rectify the problem so please bear with them."
BBC Wales said power went off in parts of Broadcasting House at about 6.15pm.
It said: "BBC Wales Today was unable to go out at its regular time of 18:30BST and BBC Radio Wales's Gareth Lewis programme fell silent."
BBC Radio Wales also experienced difficulties. It wrote on Twitter: "We’re currently experiencing technical issues. Our support teams are working on the problem and we hope to return the service as soon as possible."
BBC One Wales announced just before 9pm on Friday that it was back on air.
After power was fully restored late on Friday night a BBC Cymru Wales spokesman said: "Our technology staff are continuing to work to ensure that there is no further disruption to the services. We apologise for the problems and thank everyone for their patience.”
BBC Wales will be moving the first of 1,200 staff into its new headquarters in the centre of Cardiff in October.
