Two men were killed by an explosion as they used a blowtorch to open up a strongbox that turned out to be full of fireworks at a Hopkinton, N.H., landscaping company early Tuesday morning, cops said.

The two men were dead when cops and firefighters showed up at the scene at New Yard Landscaping on Farrington Corner Road at 1:31 a.m., after a neighbor reported hearing the blast.

Authorities did not say why the men were there but said they did not have permission to be on the property in the middle of the night.

The victims, Lucas Bourke of Allenstown, N.H., and Ethan Keeler of Epsom, N.H., both 21, were using an oxy-acetylene torch in an attempt to “gain entry to a closed metal container” filled with consumer fireworks when the box exploded, officials said.

It was unclear whether the two men knew what was in the metal box when they started heating it up.

An investigation by the Hopkinton police and fire departments, as well as state Fire Marshal J. William Degnan, is ongoing.