Volkswagen Chief Executive Martin Winterkorn speaks at the annual news conference of Volkswagen in Berlin, in this file picture taken March 12, 2015.[Photo/Agencies]

FRANKFURT - Volkswagen Chief Executive Martin Winterkorn resigned on Wednesday, taking responsibility for the German carmaker's rigging of US emissions tests.

"Volkswagen needs a fresh start - also in terms of personnel. I am clearing the way for this fresh start with my resignation," 68-year-old Winterkorn, who has been at the helm for eight years, said in a statement.

US authorities are planning criminal investigations after discovering that Volkswagen programmed computers in its cars to detect when they were being tested and alter the running of their diesel engines to conceal the true level of emissions.

"I am shocked by the events of the past few days. Above all, I am stunned that misconduct on such a scale was possible in the Volkswagen Group," Winterkorn said.

Volkswagen shares, which lost over a third of their value on Monday and Tuesday, were trading 5.3 percent higher at 111.65 euros at 5.25 p.m. (1530 GMT).

Senior members of Volkswagen's supervisory board said in a separate statement they expected further heads to roll in the coming days as an internal investigation seeks to identify who was responsible for what has turned into the biggest scandal in Volkswagen's 78-year history.

Volkswagen said on Tuesday it was setting aside 6.5 billion euros ($7.3 billion) to help cover the costs of the crisis, though analysts doubt that will be enough.