The A6120 Ring Road Farsley is blocked in both directions between Priesthorpe Road and A647 Bradford Road (Dawsons Corner) following a crash.
The incident between a car and a taxi, on Horsforth New Road in Rodley, left several people injured, police said.
Thick black smoke was spotted by residents of Farsley and Pudsey at around 5pm on Monday evening.
Danielle Dumpling, 41, was out with her son Dex, 14, when they came across the crash.
“People were helping get someone out of the car”, Danielle told the Yorkshire Post.
“I asked if Dex could see where the fire was coming from and if I needed to call 999, and he said it wasn’t coming from the field or the school, it was coming from a car on the road.
“I told him to come away and asked if there were people about, as I could see there were cars still driving past.
“He said people were helping get someone out of the car, and could hear the sirens approaching.”
Danielle posted on local Facebook forums to warn other residents to stay away from the incident before she heard a loud explosion – the emergency services were already on the scene.
“We heard an explosion and the smoke billowed up”, Danielle added.
“I just hope whoever was involved is ok, it really didn’t look good at all.”
The air ambulance is reported to have landed in the grounds of Farsley Fairfield School while dealing with the incident.
Traffic is now building in the area.
A young child has been rushed to hospital with serious injuries after the crash between a car and a taxi, police said.
In a statement, a spokesperson for West Yorkshire Police said: “Several parties were taken to hospital for treatment including a very young child who suffered serious injuries.”
Road closures have been put in place at the scene, including at Dawson’s Corner, and drivers have been urged to avoid the area while police enquiries and recovery work continue.
Yorkshire Ambulance Service and West Yorkshire Fire and Rescue Service have been asked to comment.