* Guajataca Dam could burst at any time
* Governor urges downstream communities to evacuate
* Flooding from dam would be life-threatening -weather service
By Dave Graham and Robin Respaut
SAN JUAN, Puerto Rico, Sept 24 (Reuters) - A Puerto Rico dam damaged by heavy rains from Hurricane Maria was in danger of failing on Sunday, posing a risk to communities downstream, as people across the U.S. territory sought to dig out from the deadly storm.
Some 70,000 people who live downstream from the compromised Guajataca Dam in the northwest of the island were under orders to evacuate, with the structure in danger of bursting at any time.
Puerto Rico Governor Ricardo Rossello, after surveying damage to the cracked dam, reiterated his request on Saturday that people leave the area as soon as possible.
"The fissure has become a significant rupture," Rossello said at a news conference.
The dam, which is made of earth and surrounded by trees in a largely rural region of Puerto Rico, is 120 feet (37 metres) tall, according to a U.S. Army Corps of Engineers database
The National Weather Service extended a flash flood watch for communities along the rain-swollen Guajataca River, downstream from the dam, until 1400 local time on Sunday.
If the dam fails, the flooding would be life-threatening, the National Weather Service warned. "Stay away or be swept away," it said.
Maria, the second major hurricane to savage the Caribbean this month and the most powerful storm to strike Puerto Rico in nearly a century, carved a path of destruction on Wednesday.
The storm killed at least 25 people, including at least 10 in Puerto Rico, as it churned across the Caribbean, according to officials and media reports.
It knocked out electricity, apart from emergency generators, on Puerto Rico, which has 3.4 million inhabitants.
Severe flooding, structural damage to homes and virtually no electric power were three of the most pressing problems facing Puerto Ricans, New York Governor Andrew Cuomo, whose state is home to millions of people of Puerto Rican descent, said during a tour of the island.
"We lost our house, it was completely flooded," said resident Carmen Gloria Lamb, a resident near the rain-swollen Guajataca. "We lost everything; cars, clothes, everything."
The Guajataca Dam was built in 1929 to serve as a supply of drinking water and for irrigation, according to a U.S. Geological Survey website.
FUEL SHORTAGES AND WATER RATIONING
Signs of the strain on Puerto Ricans were evident throughout San Juan, the capital.
Drivers had to wait up to seven hours at the few filling stations open on Saturday, according to news reports. Hotels, meanwhile, warned that guests might have to leave soon without fresh supplies of diesel to keep generators operating.