BERLIN - General Motors Corp plans to launch hybrid cars in Europe in around three years, GM Europe chief Carl-Peter Forster said on Wednesday.

The cars, which GM styles as "extended range electric vehicles," would run on electric power but automatically switch to a small petrol or diesel motor when the battery runs low.

The twin-power system would allow drivers to drive around town using the electric motor and make long-distance trips using the petrol or diesel engine, without having to worry about charging up the battery, Forster said.

"We are investing an enormous amount. We will launch these cars in Europe, both as Opel and as Chevrolet, in around three years," Forster told an auto conference in Berlin.

The hybrid cars would be more expensive than all-electric vehicles, but GM believed they would be more popular with consumers as they could drive further without worrying about the battery running flat.

GM is also aiming to produce its all-electric Chevy Volt by mid-September and aims to have 50 prototypes with production-ready parts by the end of 2008.

GM is designing the Volt to run for 40 miles on a lithium-ion battery pack that can be recharged at a standard electric outlet.