A two-alarm blaze at a shipping warehouse in northeast Calgary is out, but now investigators are trying to find out what caused the fire.

Crews were called to the UPS warehouse on Aero Drive N.E. when smoke was spotted leaking from a trailer at the facility.

About 20 minutes later, the package inside the shipping container burst into flames, forcing crews to call a second alarm because of the toxic black smoke.

Police blocked off a wide area so crews could take care of the fire.

The issue now is trying to figure out what was in the container and where it was headed.

“The shipping documents are actually attacked to the exterior of this trailer. Those documents were burnt up in the fire, so we’re working with the shippers right now to try and identify the product and try to find its destination,” said CFD Battalion Chief Allan Ball.

Two employees at the facility were exposed to the substance.

They’ve been assessed but will have to wait for treatment until Hazardous Materials technicians find out exactly what was inside the package.