The trial of four former Volkswagen managers accused of fraud in the "dieselgate" emissions-cheating scandal has begun in the absence of the group's ex-boss, whose day in court was delayed for health reasons.

The defendants allegedly organised commercial fraud and tax evasion in relation to the scandal.

The global car industry was rocked in September 2015, when Volkswagen admitted tampering with millions of diesel vehicles to dupe pollution tests.

Last week, the court decided to split proceedings, delaying the trial of Martin Winterkorn, the group's former CEO, for reasons of ill health.

Mr Winterkorn, 74, was initially meant to stand trial alongside the other four executives but recently underwent an operation, leaving him unable to appear.

The hearing in Brunswick, not far from Volkswagen's corporate seat in Wolfsburg, is the second significant criminal trial in relation to the dieselgate scandal.

Another, involving Rupert Stadler, the former boss of Volkswagen subsidiary Audi, began a year ago and is still ongoing.

Judges will hope to pinpoint, among the company's engineers and directors, who was aware of the emissions-cheating software, when they knew, and who gave the green light to the plan involving "nine million vehicles sold in Europe and the US", according to the indictment.

Among the defendants is Heinz-Jakob Neusser, former technical director at Volkswagen.

The other three, named by prosecutors as Jens H., Hanno J. and Thorsten D., held a variety of posts in product development, including emissions management.

In a statement around the start of the trial, Volkswagen said the scandal was "part of our history" and stressed that it had "learnt from our past".

The German car giant has already paid out damages, refunds and court fees of around €30 billion in relation to the scandal, mostly in the US.

Mr Winterkorn himself has agreed to pay €11.2m in damages and interest to his former employer in a settlement with Volkswagen.

The former CEO's hotly anticipated trial does not yet have a date, with medics unable to provide a clear timetable for his recovery, according to the court.

Mr Winterkorn faces a separate charge in Berlin of giving false testimony to a parliamentary committee looking into the scandal.