The clients each have accounts containing up to 5 million euros at the unidentified bank, the newspaper said, adding that NRW tax investigators were currently analysing the data.

The state government of NRW declined to comment on Sunday, referring to tax secrecy.

Since 2010, NRW has bought several CDs containing data of tax evaders. Since then almost 19,000 tax evaders in that state alone have declared themselves to authorities. In other federal states the number of tax evaders turning themselves in has also increased.

The newspaper also said that in the past week there had been several raids on the unreported income of clients of Credit Suisse in NRW related to a tax CD that NRW authorities bought in 2012.

A spokeswoman for Credit Suisse declined to comment.

Tax evaders who come clean before an investigation begins can currently avoid jail by paying the back tax and interest penalties but from Jan. 1, 2015, the requirements to qualify for such an exemption from punishment will be tightened.

The threshold for exemption will fall from unpaid tax liability of 50,000 euros to 25,000 euros and the penal surcharge on tax payments made in arrears will also be higher.

In March a German court convicted Bayern Munich's then-president, Uli Hoeness, of tax evasion and sentenced him to 3-1/2 years in jail.

(Reporting by Klaus-Peter Senger and Michelle Martin in Berlin and Joshua Franklin in Zurich; Editing by Alison Williams)