Arecibo, Puerto Rico: The Arecibo Observatory telescope in Puerto Rico, which once starred in a James Bond film, collapsed Tuesday when its 900-ton receiver platform fell 140 meters and smashed 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 cables that held the platform in place over the radio dish - which measures 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.
"We can confirm the platform fell and that we have reports of no injuries. We will release additional details as they are confirmed," 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" took place high above the dish, and in the film "Contact" an astronomer played by Jodie Foster used the observatory in her quest for alien signals.
'Big loss for the world'
Abel Mendez, director of the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo, said the platform fell before 8:00am (1200 GMT).
He described 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 until August this year, 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 working to determine how to assess and repair the damage 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."
"Over its lifetime, Arecibo Observatory has helped transform our understanding of the ionosphere," Michael Wiltberger, head of NSF's geospace section, said last month.
The site had hoped the dismantling plan would preserve other parts of the observatory for future research and education.