A prototype of a SpaceX rocket the company hopes will one day journey to Mars crashed in a fiery explosion as it tried to land upright after a test flight today.

It was the second such explosion after the last prototype of Starship met a similar fate in December.

"We had again another great flight," said a SpaceX announcer on live footage that was broadcast online. "We've just got to work on that landing a little bit."

The company's founder Elon Musk was uncharacteristically quiet on social media, having announced the night before he was "Off Twitter for a while."

The stainless steel rocket dubbed SN9 was cleared for lift-off from Boca Chica, Texas by the US Federal Aviation Administration (FAA), which had earlier delayed granting authorisation after determining that SpaceX's last launch violated the terms of its license.

The rocket launched smoothly around 3:30 pm local time (2030 GMT) and progressively shut down its engines as it reached a height of 10 kilometres (six miles), then performed a series of test maneuvers in a horizontal "belly flop" position.

It was when the rocket attempted to return to a vertical position for landing that the problems began, with the footage showing it came in much too fast and at a bad angle.

It landed with a deafening crash, and exploded into bright orange flames and a dust cloud, but the fire did not spread.