A 6-year-old boy who was riding with his mother's boyfriend on an illegal mini-dirt bike was killed after it was hit Sunday night by a SUV in West Philadelphia, police said.

The boyfriend was critically injured and the driver of the 2014 Jeep Compass was detained on suspicion of driving under the influence of alcohol and for operating a vehicle with a suspended license, authorities said.

The names of the dirt bike operator and the SUV driver have not been released. Neither driver has been charged pending further investigation, Capt. Mark Overwise of the Accident Investigation Division said at a Monday afternoon news conference.

The 6-year-old was identified as Malik Williams of the 500 block of North Gross Street.

Police said the 26-year-old man and and the boy were headed south on the dirt bike on 63rd Street about 11:15 p.m. when they were struck by the northbound SUV, which was making a left turn on Callowhill Street. Both drivers had the green light. Neither the man nor the boy on the dirt bike was wearing a helmet, and the bike was not equipped with any lights, police said.

The boy was taken to Children's Hospital of Philadelphia, where he died at 12:13 a.m. Monday, police said. The dirt bike operator was taken in critical condition to Lankenau Medical Center. He lost his left leg as a result of the crash, Overwise said.

The SUV driver remained at the scene. Police said he appeared impaired and could face DUI charges.

The man with whom the boy was riding also could face charges, such as endangering the welfare of a child and recklessly endangering another person, Overwise said.

"That requires further investigation. It will be up to the District Attorney's Office," he said.

Overwise emphasized that it is illegal to ride dirt bikes on city streets.

"Absolutely, it's a problem," especially in nicer weather, he said.

"It's a dangerous thing to drive it on the street; it's also dangerous to chase them," Overwise said. He added that if people see dirt bike riders, "they should call 911 or they should pull over" if they are driving.

This dirt-bike fatality was the first this year. Last year, two people, ages 17 and 18, were killed in dirt-bike crashes, Overwise said.

"People who drive these absolutely have no regard for your safety," he said.