A hazardous materials response team was dispatched to Texas Senator Ted Cruz’s campaign office in Houston on Tuesday morning to investigate a mailed envelope that contained a white powdery substance, the campaign confirmed to THE WEEKLY STANDARD.

Multiple fire trucks and at least one hazmat truck were spotted on the scene after the letter was opened by campaign staff and reported to authorities.

At time of publishing, it was unclear whether the substance was found to be toxic or not.

Update, October 2, 2018, 1:08 p.m.: Houston Fire wrote on Twitter that two people had been taken to the hospital after being exposed to the substance:

Update, October 2, 2018, 2:18 p.m.: Houston Fire reports that the office has been deemed clear:

This post will be updated with new developments as they happen.