Clouds of space junk orbiting the Earth have reached a dangerous "tipping point", threatening to smash satellites and endanger astronauts, US scientists warned in a study this week.

"The current space environment is growing increasingly hazardous to spacecraft and astronauts," said Donald Kessler, chair of the committee that wrote the report and retired head of NASA's Orbital Debris Program Office.

"NASA needs to determine the best path forward for tackling the multifaceted problems caused by meteoroids and orbital debris that put human and robotic space operations at risk."

NASA is currently tracking over 22,000 pieces of debris and estimates there are millions more that are too small to track.

Among those are at least 500,000 particles of up to 10 centimeters (four inches) in diameter, which can still cause damage when traveling at such high speeds.

Computer models have shown that the "debris has reached a 'tipping point,' with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures," the National Research Council said in a statement Thursday.

Efforts to limit the amount of space debris suffered a major setback in 2007 when China tested its anti-satellite missiles on a weather satellite which was blown to pieces.

More debris was formed two years later when two satellites accidentally collided in orbit.

Cleaning up the spent rockets and abandoned equipment is not simply costly -- it is also complicated by the fact that the United States is prohibited by international law from collecting objects belonging to other nations.

"The Cold War is over, but the acute sensitivity regarding satellite technology remains," explained committee vice chair George Gleghorn, former vice president and chief engineer for the TRW Space and Technology Group.

The 160-page report recommends that NASA engages the State Department's help in sorting out the "economic, technological, political, and legal considerations."