Police have declared that damage to the world's first solar-power highway, in eastern China, was caused by vehicles, not vandals.

Authorities in Jinan, Shandong province, said the photovoltaic road, which extends for intervals of 100 meters, was damaged by the undercarriages of cars impacting the road's surface on a downhill section.

The initial belief that the problem was caused by vandals or thieves has been rejected, as the surface is too tough and the damage is not consistent with it being cut by a machine, city police said on Monday.

The 1.12-km solar expressway, in the southern part of Jinan's ring road system, was opened for testing on Dec 28. The road has three layers: transparent and weight-bearing concrete on top, solar panels in the center and insulation on the bottom.

Jinan police were notified of the damage just five days after the highway opened. Part of the protective layer of a solar panel, measuring about 1.85 meters by 10 centimeters, was discovered missing during a routine check.

The highway is designed for public transportation and electricity generation, Zhang Hongchao, a project designer and transportation engineer with Tongji University told China Central Television.

Zhang said it can handle 10 times more pressure than a standard asphalt road and is expected to generate 1 million kilowatt-hours of electricity annually, helping to power streetlights and melt snow.

The road is also designed to supply power to charge electric vehicles.

US-based scientists Scott and Julie Brusaw first raised the idea of solar roads in 2006. Eight years later, the Netherlands built the first pedestrian and bike path embedded with solar panels.

In 2016, a French village opened the world's first solar-panel road, stretching 1 km.

Li Shun contributed to this story.