MEXICO CITY: A passenger bus plunged into a ravine in Mexico's Nayarit state, killing 18 people, local authorities said.

Among the dead were three minors, with 22 others injured, local media said, citing Jorge Benito Rodriguez, Secretary of Security and Citizen Protection of Nayarit, reports Xinhua news agency.

According to local reports, the bus was traveling from Mexico City to Tijuana on the border with the US.

It fell into the ravine about 50 meters deep along the north bypass of Tepic.

Rescue efforts were "extremely" complicated due to the location, said Rodriguez, adding that state police and firefighters, in coordination with the Mexican Red Cross and other agencies, were on the scene.

The cause of the accident remains unknown, he said.