The Mexican government is rushing help to 1.2 million people devastated by floods in the south, struggling to reach thousands of settlements cut off for as much as a week.
Thousands remain isolated more than five days after rivers washed away their homes, crops and many of their neighbours. Many people are growing increasingly angry at the pace of relief efforts in the devastated coastal regions.
Mexico's Defence Secretariat said helicopter aid flights to isolated communities had continued despite clouds and rain, even though other officials told the government news agency Notimex that some flights had been cancelled.
"We are doing everything possible to reach all of the communities," said Lieut Col Edgar Novelo, an army surgeon helping oversee medical aid efforts in Huixtla, 30 miles from the Guatemalan border.
The floods in the southern state of Chiapas could be one of the deadliest natural disasters to hit Mexico this century.
A report, prepared by officials on the ground in Chiapas, one of Mexico's poorest states, said 407 people had been reported dead and another 849 corpses could be buried under a great sea of mud that has swept away dozens of communities.
Mexico's Red Cross continued to call for donations of food and medicine. Among those responding was Pope John Paul II, who donated £30,000 through Catholic charities for Mexico.