Emergency crews are responded to injury crash involving a semi near Mustang, Oklahoma. 

According to authorities, the crash occurred on Highway 4 near Mustang Road when a semi and a vehicle carrying a horse-trailer collided. 

At least three people have been transported to a local hospital and their conditions are unknown. 

At this time, there's no word yet on what caused the crash.  

This is a developing story. Stay with News 9 for updates.