CHENGDU, July 10 (Xinhua) -- Heavy rain caused a section of a national highway to collapse in southwest China's Sichuan Province Tuesday, according to local traffic police.

Parts of the road surface cracked and collapsed at around 4 a.m. Tuesday in Wenchuan County. A van was trapped on the collapsed road, while a truck turned on its side. No casualties have been reported yet.

The highway is one of the key routes toward the Tibetan and Qiang Autonomous Prefecture of Aba. Traffic police quickly cordoned off the section and suspended traffic.

China's national weather observatory issued a yellow alert for rainstorms Tuesday, as heavy rain will sweep across parts of the country.

China has a four-tier color-coded weather warning system, with red the most severe, followed by orange, yellow and blue.