Shares in Wirecard sank more than 20% in early trading on Tuesday after the Financial Times newspaper published documents on the company's accounting practices alleging an effort to inflate sales and profits, dealers said.
At 0806 GMT, shares were down 15% after hitting their lowest since April 24, making them the biggest faller on Germany's DAX 30 and on track for their worst day since early February.
A Wirecard spokesman declined to comment on the report.
The newspaper said the documents included internal company spreadsheets and related correspondence between senior members of Wirecard's finance team, which appear to indicate an effort to inflate sales and profits at its businesses in Dubai and Ireland, as well as to potentially mislead EY, its tier-one auditor.
The report comes after the paper published a series of stories earlier this year alleging fraud and false accounting at Wirecard's Singapore office and that a key Middle East unit was not properly audited.
The company has denied the FT's allegations, saying that although Dubai-based subsidiary Card Systems was not individually audited, its books had undergone higher-level "full-scope" scrutiny by auditor EY.