Mexico is going through its toughest rainy season in recent memory. The rains have already caused floods that have killed 20 people.
From the Guardian, writer Jo Tuckman describes this latest disaster.
The state's governor, Ulises Ruiz, said heavy rains had caused a 200 metre (656ft) wide chunk of hillside next to the town of Santa María Tlahuitoltepec to collapse.
"There could be 500 or 600 people [dead] – perhaps 1,000," Ruiz told the Televisa television channel, adding that between 100 and 300 homes had been buried by the landslide.
It happened at about 4am when most people were asleep in their homes, potentially increasing the scale of the tragedy.
Donato Vargas, a local official, said 500 people were missing.
"We were all sleeping, and all I heard was a loud noise ... when I left the house, I saw that the hill had fallen," he said, adding that he had called the Mexican army and state officials for help.
"It has been difficult informing authorities because the road are very bad and there isn't a good signal for our phone."
Ruiz said rescue workers were on their way to the area by air and should be able to provide a more accurate estimate of the area affected and the number of casualties when they got there.
"We haven't reached the location yet," he said, explaining that bad weather and blocked roads were hampering the rescuers.