CONCORD, N.H. (AP) — A three-day drill involving multiple New Hampshire and federal agencies will test how local, state and federal authorities deal with possible terrorist attacks.

The drill begins Wednesday with delivery of a package containing a ‘‘toxic’’ substance to the Statehouse annex mail room. The drill is to test how authorities identify the substance and deal with the potential crisis.

Separate mock terrorist events are planned for Thursday and Friday to test emergency workers.