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:

Two people were taken to the hospital after apparently being exposed to a white powdery substance in an office building at 3200 SW Fwy. The 9th floor of the Phoenix Tower has been evacuated as HFD HazMat is responding to the scene working to determine the nature of the substance.

— Houston Fire Dept (@HoustonFire) October 2, 2018

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

The evacuation order has been lifted for the office building at 3200 SW Fwy. All tests were negative for any hazardous substance.

— Houston Fire Dept (@HoustonFire) October 2, 2018

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