SpaceX appealed for help from the public and US government agencies on Friday in the investigation of what made a Falcon 9 rocket explode last week during a launch test.

No one was hurt in the September 1 blast, which happened as the rocket was being fueled ahead of a standard, pre-launch test known as a static-fire at Cape Canaveral, Florida.

"Still working on the Falcon fireball investigation," SpaceX CEO Elon Musk wrote on Twitter.

"Turning out to be the most difficult and complex failure we have ever had in 14 years."

Musk, a billionaire entrepreneur who rose to fame as the co-founder of PayPal, added that the blast happened "during a routine filling operation."

"Engines were not on and there was no apparent heat source."

According to video footage of the incident, the SpaceX rocket and an Israeli communications satellite, Amos-6, suddenly burst into a massive fireball amid what appeared to be a succession of blasts.

"Particularly trying to understand the quieter bang sound a few seconds before the fireball goes off," Musk wrote.

"May come from rocket or something else."

He said "support and advice" from the US space agency NASA, the Federal Aviation Administration, and the US Air Force would be "much appreciated."

The California-based company also issued an appeal to the public.

"Please email any recordings of the event to [email protected]."

The accident -- the second of its kind since SpaceX was founded in 2002 -- came just over a year after a Falcon 9 rocket exploded after liftoff on June 28, 2015, destroying a Dragon cargo capsule bound for the International Space Station (ISS).

Before that, SpaceX had logged 18 successful launches of the Falcon 9 -- including six of 12 planned supply missions to the ISS carried out as part of a $1.6 billion contract with NASA.