German carmaker Volkswagen has pleaded guilty to criminal charges in the emissions-cheating scandal, closing an important chapter in the saga that has rocked the company since 2015.

The company in January agreed to plead guilty and pay $4.3 billion (€4.03 billion) in criminal and civil fines to settle charges that it defrauded the United States and conspired to violate the Clean Air Act by installing so-called defeat devices on diesel-powered cars that evaded emissions standards.

"Volkswagen deeply regrets the behaviour that gave rise to the diesel crisis," Volkswagen spokeswoman Jeannine Ginivan said in a statement.

"The agreements that we have reached with the US government reflect our determination to address misconduct that went against all of the values Volkswagen holds so dear."

The settlement with the Justice Department also requires the company to hire an outside compliance monitor for three years.

The guilty plea entered today is in addition to $17.5 billion (€16.4 billion) that the company already agreed to pay in settlements with car owners, dealers and for environmental cleanup.

One aspect of the case that remains unresolved is the fate of VW executive Oliver Schmidt who US authorities arrested in Miami in January, one of six company officials charged in the matter.

Prosecutors this week rejected defence arguments that Mr Schmidt should be released pending the outcome of his case and described him as a flight risk.

The other five company officials charged are believed to be in Germany.

Regulators in 2015 discovered that Volkswagen diesel cars marketed as clean in fact spewed up to 40 times the permissible limits of nitrogen oxide during normal driving, but this was hidden during emissions testing.

As many as 11 million vehicles sold worldwide were configured to cheat emissions tests.

The company developed the illegal technology in 2009 and, according to court documents, prosecutors believe senior employees attempted a cover-up after learning of the illegal technology in 2015.