Two trains collided head-on in Switzerland on Monday evening, injuring about 35 people, five seriously, police said.

The driver of one of the trains was still unaccounted for and thought to be inside the wreckage, at Granges-près-Marnand in the canton of Vaud, police spokesman Jean-Christophe Sauterel said.

"These are regional trains. The speeds are a little lower and even if one deeply regrets the likely loss of life of one person as well as five serious injuries, the situation could have been much more catastrophic," Sauterel said.

He said it was too early to try to ascertain the cause of the crash.

One of the injured was taken by helicopter to Lausanne. Others were treated on the spot by paramedics or taken to hospital by ambulance.

About 40 people were on the two trains, one of which was heading to Lausanne, the other was going to Payerne.

Seventy-nine people were killed in a train crash in Spain last week, one of the worst in decades. - Reuters