The celebrated Arecibo Observatory telescope in Puerto Rico, which once starred in a James Bond film, collapsed Tuesday when its 900-ton receiver platform plunged 450 feet (140 meters) onto the radio dish below.
Engineers had recently warned of the huge structure's decrepit condition, and the US National Science Foundation (NSF) announced only last month that it would be dismantled.
Two of the cables that held the platform over the radio dish -- which measures 1,000 feet (300 meters) in diameter -- had snapped this year, and the structure finally gave way on Tuesday morning.
Photographs showed clouds of dust rising into the air and the remains of the telescope instruments scattered across the site.
"We can confirm the platform fell and that we have reports of no injuries," Rob Margetta, spokesman for the NSF, told AFP.
The telescope was one of the largest in the world and has been a tool for many astronomical discoveries since the 1960s, as well as being famous for its dramatic scale and setting.
An action scene from the Bond film "GoldenEye" featuring Pierce Brosnan took place high above the dish, and in "Contact," an astronomer played by Jodie Foster used the observatory in her quest for alien signals.
Abel Mendez, director of the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo, said the platform fell sometime before 8:00 am (1200 GMT), describing it as "a total disaster."
"Many students are trained in astronomy in the observatory, they are inspired like me to do a career in science and astronomy," he said.
"The loss of the Arecibo telescope is a big loss for the world, but it is more of a loss for Puerto Rico. It is an icon for our island."
The telescope was in operation for 57 years until August, and scientists had lobbied the NSF to reverse its decision to close the site.
In August, an auxiliary cable failed after slipping from its socket in one of the towers and left a 100-foot gash in the dish below.
Engineers were assessing the damage and how to repair it when a main cable connected to the same tower broke on November 6.
Before Tuesday, a controlled demolition had been planned to avoid an unexpected collapse.
Among the telescope's successes was in 1992 discovering the first exoplanet -- a planet outside the solar system -- and in 1981 it helped produce the first radar maps of the surface of Venus.
The observatory's website said the telescope was "a world-leading radio astronomy, solar system radar and atmospheric physics facility, contributing highly relevant data to support discovery, innovation and the advancement of science."
"What a sad day for Astronomy and Planetary science worldwide and one of the most iconic telescopes of all time," tweeted Thomas Zurbuchen, associate administrator at the NASA science mission directorate.
The site had hoped the dismantling plan would preserve other parts of the observatory for future research and education.
"As we move forward, we will be looking for ways to assist the scientific community and maintain our strong relationship with the people of Puerto Rico," the NSF said in a tweet.