Discussions about shifting some production to VW's Emden plant have started again within the parent company's management, the unions said in a statement.

"The (unions') committee categorically rejected the possibility of moving Superb car production to another location outside the Czech Republic," they said in the statement, published in their weekly newsletter on their website.

A Skoda spokesman said the carmaker was looking at ways to expand production.

"Currently we see several options, like the already announced expansion of the KAROQ model assembly to Osnabrueck (in northwest Germany). Besides this, there are no other changes planned for the Skoda brand at the moment," Tomas Kotera said in a response to an emailed question.

Volkswagen spokeswoman Leslie Bothge said the company would not comment on "speculation".

The German car group has been looking at ways to boost production at its Czech carmaker to keep up with robust demand.

Once the butt of jokes, Skoda has flourished under nearly 30 years of VW ownership to become one of its profit drivers, even beating luxury brand Audi's and BMW's operating margins last year.

A VW labour official told Reuters in June that further steps would be needed to boost output at Skoda, even though some production is already being shifted to Germany to relieve its stretched Czech factories.

In Thursday's statement, Skoda union leader Jaroslav Povsik said the Superb is a flagship model and "part of our DNA".

"We have to find a solution to fight for Superb, which is important for all of us," Povsik said. "It creates profit that we would miss."

(Reporting by Robert Muller, editing by David Evans and Gareth Jones)