The area of the recent Chinese invasion of Vietnam has been devastated and three major towns in the region are in ruins.

A three-week tour of the frontier battle zone revealed that bridges have been blown up and roads have been mined or destroyed everywhere.

In the towns of Lao Cai, Lang Son and Cao Bang, the hospitals were demolished. Eigthy percent of the buildings were destroyed and all electric poles ahve been toppled. Electricity has been cut off and water is in short supply.

It would be impossible to determine how much of the damage was caused by Chinese troops and how much by Vietnamese soldiers trying to repel the invaders.

Correspondents visiting the area saw what appeared to be mass graves of village in the Cao Bang area.

Surviving villagers evacuated during the fighting have begun regrouping to await permission to return to the area.

Meanwhile, it was clear that the entire population of northern Vietnam is being mobilized for additional fighting.

Rallies and meetings are held late into the night and endless processions of soldiers are moving to take up positions in the valleys and mountains along the Chinese frontier.

AFP correspondent Jean-Pierre Gallois reported the following from Phnom Penh, the capital of Cambodia .

Despite promises of the new Vietnam-backed government, to move Cambodians back to their old homes, Phnom Penh remains a ghost town.

The war-ravaged buildings housing the National Bank of Cambodia are surrounded by a carpet of banknotes of riels, the old currency. Factories, public buildings and the railway station are empty.

Only the Ministry of Defense, with the flag of the new government flying overhead, is back in use.

Pochentong Airport is quiet with only a few military transport planes and artillery pieces lined up along the runway.

About 3,000 officials and their families have been permitted to return to the city, once the home of almost 3 million people.