A series of four related accidents that left seven people dead and at least 15 injured on the Mexico-Cuernavaca toll highway Sunday were likely caused by extreme speeding, the federal highways agency (Capufe) said.

In total 13 motorcycles, two tractor-trailers, a white pickup truck and at least 12 other vehicles were involved in the crashes which closed the highway for five hours in the direction of Morelos.

The first crash occurred when a motorcycle crashed at full speed into the back of a pickup truck that had stopped in the middle of the highway after traffic had backed up and come to a halt.

That caused the second accident: another motorcyclist tried to brake about 500 meters farther up the highway so he and his passenger could help their fellow riders. The rider lost control and crashed into a vehicle, flying five meters before hitting the ground.

Moments later, another couple on a motorcycle lost control and were trapped under a tractor-trailer that could not brake in time. They were crushed by the trailer’s rear tires.

The crashes caused a pileup which left another15 people injured. Seven were taken to hospitals in Cuernavaca and were reported as stable in the latest medical reports, according to the newspaper El Universal.

A motorist driving a sports car, Carlos Rosete, admitted in an interview with television channel Foro TV that he had been racing one of the motorcyclists shortly before a crash. “We came through the toll plaza and I came through next to the motorbike … we were traveling at 250 [kilometers per hour], we were running races … I lost sight of them and they crashed behind the white pickup truck,” he said.

Numerous comments on Twitter revealed that racing motorcycles are common on the highway on weekends yet there is no enforcement of speed limits. The limit where the accidents took place is 110 kph.

With reports from El Universal