Police say the incident happened at around 5 p.m. Wednesday evening at West 45th Street and 9th Avenue.
Videos captured by onlookers show the 14-year-old horse, Ryder, lying motionless on the hot asphalt.
New York City police officers placed a pillow under his head, cooled him down with a spray hose, and gave him a shot of adrenaline before he regained strength.
Transport Workers Union Local 100, the group that represents horse carriage drivers, says Ryder made it safely into his trailer where he was examined by an equine veterinarian.
The doctor believed the horse may have been suffering from equine protozoal myeloencephalitis, a neurological disease caused by infected opossum droppings.
A union spokesperson urged people not to panic or jump to conclusions.
However, animal advocacy group NYCLASS argued the incident was caused by heat exhaustion and told FOX 5 News in a statement: "NYCLASS has learned that yet another carriage horse has collapsed on the streets of New York City in traffic. This disturbing incident in front of dozens of horrified onlookers occurred during the evening rush hour. How many more incidents like this do we need? This is clearly animal abuse and it must be stopped."
In 2019, the City Council passed a law making it illegal for horse-drawn carriages to operate when temperatures reach 90 degrees, or whenever it’s 80 degrees or above with an equine heat index of 150 or higher. It was unclear what the exact conditions were at the time of the incident on Wednesday.
Last month, New York City Council member Bob Bolden introduced legislation that would block new licenses and replace horse-drawn carriages with electric carriages.
Holden responded to the incident with a tweet reading in part, "Drivers would be able to work year-round and earn more. Drivers and horses deserve better."
Mayor Adams has yet to publicly endorse bans on horse carriages but has condemned similar incidents.