The Asahi newspaper reported on its website that prosecutors had begun searching the offices of Nissan’s headquarters and other locations on Monday evening.
The Tokyo district public prosecutors office declined to comment.
An ouster of Ghosn, 64, is bound to raise questions about the future of the alliance that he personally shaped and had pledged to consolidate with a deeper tie-up, before eventually stepping back from its operational leadership.
Renault shares tumbled 13 percent in Paris to be among the worst performing stocks in Europe. Nissan’s German-listed securities plunged 12 percent.
Brazilian-born, of Lebanese descent, and a French citizen, Ghosn began his career at Michelin in France, moving on to Renault. He joined Nissan in 1999 after Renault bought a controlling stake and became its CEO in 2001. Ghosn remained in that post until last year.