Two aircraft - a Boeing B-17 bomber and a smaller plane - collided mid-air at an air show at Texas's Dallas Executive Airport on Saturday, immediately falling to the ground and bursting into flames.

The condition of the pilots in both the aircraft is yet to be determined, the US Federal Aviation Administration (FAA) was quoted as saying.

Dramatic visuals captured by people attending the airshow show the bigger B-17 bomber flying, not very high from the ground, in a straight line, while the smaller plane - a Bell P-63 Kingcobra, hurtling in its direction from the left. The smaller plane crashes on top of the B-17, a World War II-era plane, and immediately the two aircraft break apart into pieces, visuals show.

Within a couple of seconds, the planes are on the ground, covered in a ball of fire.

The collision occurred during the Commemorative Air Force Wings Over Dallas show, Associated Press reported, adding that the FAA and the National Transportation Safety Board were launching investigations.

In a tweet, Dallas Mayor Eric Johnson said that there were still details that remained "unknown or unconfirmed".

"As many of you have now seen, we have had a terrible tragedy in our city today during an airshow. Many details remain unknown or unconfirmed at this time. The National Transportation Safety Board has taken command of the crash scene with Dallas Police Department and Dallas Fire-Rescue continuing to provide support," he said.

The B-17, a four-engine bomber, played a major role in winning the air war against Germany in World War II. With a workhorse reputation, it became one of the most produced bombers ever. The P-63 Kingcobra was a fighter aircraft developed during the same war by Bell Aircraft but used in combat only by the Soviet Air Force.

One of the last major crashes of a B-17 was on October 2, 2019, when seven people died in an accident at an airport in Windsor Locks, Connecticut.