When will local reference be cleared if not created inside native method?

I initialized a JavaVM by CreateJavaVM and got a JNIEnv by jvm->GetEnv, and created some local references by FindClass, NewObject or CallObjectMethod etc.

In the JNI online doc, it says

In most cases, the programmer should rely on the VM to free all local references after the native method returns.

I was wondering will those local references be cleared automatically, or should I clear them manually by DeleteLocalRef or PopLocalFrame?