Shares in Takata Corp fell more than 4 percent on Friday, reversing earlier gains after a newspaper reported that the Japanese auto parts maker had concealed the risks of potentially defective air bags following an accident in 2004.

The New York Times reported Takata had secretly conducted tests on 50 airbags retrieved from scrap yards after the accident in Alabama, with results showing cracks in steel inflators in two of the air bags.

Citing two former Takata employees, the paper said Takata executives ordered the lab technicians to delete the test data instead of alerting federal safety regulators to the possible danger.

Takata could not immediately be reached for comment.

Takata shares fell as much as 4.7 percent in morning trade in Tokyo, while the benchmark Nikkei average was up 0.7 percent.