According to the Associated Press and Spain’s EFE news agency, the bus was traveling on the BV-5114 road in Fogars de Montclús, about an hour’s drive northeast of Barcelona, on Sunday when it veered off the road and plunged down a steep slope.

The country’s emergency medical service dispatched 33 ambulances and three helicopters to treat 87 people, according to an alert issued by the agency. Seven people were in serious condition, while the remaining passengers sustained less serious or minor injuries.

Olga Pané, health minister in the Catalan government, told the Associated Press that rescue teams continued searching the area to ensure there were no additional victims. The agency also reported that specialized mountain rescue teams had been deployed.

EFE reported that local police were investigating whether the bus had been carrying an excessive number of passengers, some of whom were standing at the time of the accident.

According to the news agency, a fire department official told reporters that the bus driver had tested negative for drugs and alcohol.

Catalonia’s police said in a statement that the investigation into the cause of the accident was ongoing.

According to EFE, a crane arrived at the scene on Monday to recover the bus from the slope.