The responding officers smelled "what we believe is fentanyl," CHP Officer Andrew Barclay told NBC News, and the driver was immediately treated with the narcotic overdose spray Narcan "to bring him back." Fentanyl is a powerful synthetic opioid that can be fatal even in small doses.

That officer was also given Narcan and Barclay said that treatment "likely saved his life.".

Later, a tow trucker driver, three more CHP officers and a Golden Gate Bridge patrol officer also fell ill and were treated at a hospital on Sunday, officials said.

All of those first responders had been released from the hospital by Sunday night, authorities said