Opel and its sister company Vauxhall are expected to delay the introduction of the Ampera extended-range hybrid car in the wake of battery fires after crash tests in the US.

This is despite the car being awarded a top 5-star rating in the latest round of Euro NCAP test results, announced last week.

GM and US safety regulators are trying to determine why two of the car’s lithium-ion batteries caught fire a week or more after being crash-tested by the National Highway Traffic Safety Administration (NHTSA). GM says the batteries can be made safe by draining the power from the batteries after a severe crash.

The Ampera is a slightly restyled version of the Chevrolet Volt; it was scheduled to go on sale in Europe by the end of the year and in the UK next year.

GM is reported to have postponed a planned production boost in December at the Detroit plant that makes the Volt and Ampera. The facility was scheduled to double output to 3,200 cars a week to meet the expected rise in demand with Ampera sales starting in Europe.

Mark Reuss, president, GM North America, said the company would take every precaution to assure the driving public of GM’s commitment to the safety of the Volt being handled after a severe incident and the total satisfaction of everyone who owned one.

“The Volt is a five-star safety car.  Even though no customer has experienced in the real world what was identified in this latest testing of post-crash situations, we’re taking critical steps to ensure customer satisfaction and safety,” Reuss said.

“The question is about how to deal with the battery days and weeks after a severe crash, making it a matter of interest not just for the Volt, but for our industry as we continue to advance the pursuit of electric vehicles.”

“It’s not nearly as a big a deal as the media want it to be,” said Aaron Bragman, an analyst with IHS Automotive. “There is very little threat to anyone from these vehicles. There is more of a threat involved in carting around 15 gallons of highly flammable liquid.”

Euro NCAP is the latest third-party organization to give the Volt top marks. In April 2011, the U.S. Insurance Institute for Highway Safety (IIHS) named the car its ‘Top Safety Pick’ while the NHTSA awarded the car a five-star rating.