Authorities in Texas are baffled after being flooded with reports of burning debris falling from the sky.

Terrified onlookers were heard screaming when the mysterious "fireballs" were filmed mid-morning on Sunday.

They were captured by television cameras recording a marathon in the state capital Austin.

No one has explained where the debris has come from, amid numerous reports of sightings to the Federal Aviation Administration.

The city's Sheriff's Office sent up a helicopter to investigate but it returned with no hard evidence.

There were initial concerns the fireballs originated from a collision of two space satellites last week. A US and a Russian communication satellite smashed together 500 miles above Earth.

But US Strategic Command has since said the two incidents are unrelated.

The Federal Aviation Administration said it had warned pilots to be aware of possible space debris following the satellite collision.

Russia's Mission Control chief said clouds of debris will circle the planet for thousands of years and threaten numerous satellites.

The debris field from the collision is described as huge but scientists are still trying to determine the full scope of the crash.