RTE, the French power distributor, estimated that around 5 million people were hit in France alone. Austria, Belgium, Italy, the Netherlands, Spain and Morocco were affected as well as the power imbalance was felt across the whole European grid.
The outage took place at around 21:30 GMT in Northwest Germany after power generator E.ON shut down a high-voltage transmission line over a river to let a ship pass safely.
The incident created a "brutal imbalance" in generation which was automatically compensated by a European solidarity mechanism, according to RTE. "Despite the outages, we were able to avoid a total blackout," in the whole of Western Europe, said RTE President André Merlin.
The precise sequence of events is still being investigated, said the Union for the Co-ordination of Transmission of Electricity (UCTE), which co-ordinates transmissions-system operators in 23 European countries.
The outage highlighted the vulnerability of the interconnected European grid and re-launched the debate over the necessity of building new electricity infrastructure.
French Industry Minister François Loos told France Inter radio that the incident showed the importance of electricity investments at European level. Italy's Prime Minister Romano Prodi said it showed the need for a European power regulator. "We still don't have a European energy policy," he told reporters.
Concerns over lack of investment in infrastructure and interconnections were expressed several times recently at European level. An EU directive was adopted in 2005 to deal with the issue. But EU heads of state, at a spring summit this year, rejected the idea of a single European energy regulator as "premature".
