© Weather NationEarlier, Puerto Rican authorities had scrambled to evacuate as many as 70,000 people after the National Weather Service warned that failure of the dam was 'imminent' and could lead to 'life-threatening' flash flooding.
Water was seen sweeping through the municipalities of Isabela and Quebradillas after the dam sustained structural damage from Hurricane Maria.
Nearly 16 inches of rain fell in the area, significantly raising water levels on the 90-year-old dam.
Earlier, Puerto Rican authorities had scrambled to evacuate as many as 70,000 people after the National Weather Service warned that failure of the dam was 'imminent' and could lead to 'life-threatening' flash flooding.
The National Weather Service first learned of a 'contained breach' during a Friday afternoon inspection and said a full breach would result in large peak flows that could reach the coast in under 12 hours.
Comment: Meanwhile officials are rushing to evacuate tens of thousands of people from their homes in western Puerto Rico after Hurricane Maria inflicted structural damage on a dam and unleashed "extremely dangerous" flash floods.
Some 70,000 residents in the municipalities of Isabela and Quebradillas were being evacuated by bus after a crack appeared in the nearly 90-year old Guajataca dam.
"It's a structural failure. I don't have any more details," Governor Ricardo Rossello said from the capital, San Juan. "We're trying to evacuate as many people as possible."
"This is an EXTREMELY DANGEROUS SITUATION. Buses are currently evacuating people from the area as quickly as they can," the US National Weather Service tweeted on Friday .
In a later message, the NWS tweeted: "All Areas surrounding the Guajataca River should evacuate NOW. Their lives are in DANGER! Please SHARE!"
More than 15in (nearly 40cm) of rain has fallen on the mountains surrounding the Guajataca dam, swelling the reservoir behind the nearly 90-year-old dam, which holds back a manmade lake covering about two square miles (five square kilometres).