BEIJING — Chinese state media said on Thursday that a military history buff found a collection of confidential documents related to the East Asian country's military in a pile of old papers he bought for less than $1.

The collector reported the documents to security units after recognizing their sensitive nature.

The reports didn't say what the documents were or whether anyone had been arrested, other than to say two people involved in the secondhand book and magazine business were being questioned.

The purchaser, identified only as a retiree surnamed Zhang, is an avid fan of military history and soon realized that the items contained information stamped as confidential.

China's opaque state security bodies and the Communist Party-controlled legal system often make it difficult to tell what is considered a state secret.

Chinese and foreign consultancies operating within the country have been placed under investigation by state security bodies for possessing information about the economy that in other countries would be considered part of the public record.

China's military has grown massively in recent years, and it now boasts the world's largest navy, an air force with cutting-edge stealth fighters, and a gigantic missile force that appears intended to back the country's claims to the self-governing island of Taiwan, the South China Sea and disputed islands controlled by Japan, and ultimately driving its major rival, the United States, out of the region.

In response, the US has strengthened ties with allies such as Australia, the Philippines, Japan and South Korea, while boosting arms sales and military cooperation with Taiwan.