A powerful tropical storm has struck Guatemala, bringing torrential rains that have added to the disruption caused by an erupting volcano.

Agatha, the season's first tropical storm,  has killed at least 12 people and left 11 people missing, as rain, mudslides and floods forced more than 3,000 people to flee their homes, officials have said.

The torrential rains are complicating efforts to clear up ash from the Pacaya Volcano, which began erupting on Thursday, covering Guatemala City with ash and forcing the closure of the capital's international airport.

Agatha - the first named storm of the Pacific Hurricane season - is expected to dump at least 75cm of rain on Guatemala, as well as El Salvador and southeastern Mexico.

Among the dead were four children who were buried alive when a mudslide crushed their home in San Jose Pinula, 17km east of the capital, the National Disaster Agency (Conred) said.

Elsewhere in the capital, four people died and 11 were missing after floods swept through their homes as the storm front's outer fringes lashed western Guatemala with rainfall.

Twelve Austrian tourists were rescued from a resort area that was cut off.

Ash fallout

"We have 3,377 people affected by the storm, with 574 homes damaged by rains brought by storm Agatha," David de Leon, a Conred spokesman, said.

It is feared that the rains will turn the volcanic ash from Pacaya into cement-like mud [AFP]

He said the eye of the storm was expected to make landfall overnight along  Guatemala's western coast, bringing even heavier rains and stronger winds on Sunday.

"We believe Agatha could wreak more damage in the country than tropical storm Mitch (1998) and Hurricane Stan (2005)," Ronaldo Robles, the spokesman for Guatemala's President Alvaro Colom, said.

Colom earlier said the government was considering putting the entire country under a state of emergency, extending one he declared on Friday in an area around the Pacaya volcano.

Hundreds of people are in shelters after the Pacaya erupted on Thursday, billowing clouds of ash that has blocked drainage systems.

Officials fear the rains will turn the black volcanic ash into cement-like mud.

The ash fallout has closed the country's biggest airport in Guatemala City for five days.