United States officials say forest fires in Mexico have caused the worst environmental damage of its kind they've ever seen.

A US delegation presented their findings after visiting the Chimalapas nature reserve, one of the worst-hit areas.

One official warned that hundreds of rare plants were on the verge of extinction, and many valuable species of wildlife at risk.

The BBC Mexico correspondent says the US officials painted a far bleaker picture than the Mexican government, which has been criticised for its slow response to the disaster.

More than a hundred fires continue to burn out of control across the country.