Guatemala City: Torrential rains from a tropical depression caused mudslides that have killed at least 28 people in Guatemala - most of them in separate disasters along the same highway.

The first highway slide near midday on Saturday partially buried a bus under tons of mud at kilometer marker 81 on a highway leading northwest of the capital toward Mexico.

Officials said at least 12 people died. That led President Alvaro Colom to declare a national emergency. He said four children and two adults were buried in other slides elsewhere.

"It is a tragic day. Today alone 18 people have died, 12 buried by a hill when the traveled in a bus," Colom told a news conference.

The president told officials to close the highway for fear of more slides.

"There are several hillsides that are loose and could fall. So we ask the population to not go out, to avoid moving along the highways," he said.

But hours later, vehicles were trapped by another slide at kilometer 171, officials reported, and some of the people who came to rescue them were themselves caught by following slide.

Civil Defense director Sergio Cabanas said at least 10 people were killed - some in vehicles and some among people who came to rescue them. He said at least 60 people are missing.

Regional fire department Major Otto Mazariegos told reporters that some of the victims of the second slide were rescuers.

"We are told that there are 150 missing," he said. "Under the earth there is a bus that carried we don't know how many people, and there are those who tried to help the victims of the first slide."

Heavy rains from Tropical Depression 11-E have pelted Guatemala for days, unleashing deadly mudslides in several areas, cutting highways and forcing officials to evacuate thousands of people.