A double tornado that devastated the town of Pilger in Nebraska was unusual but not unprecedented, experts say.

The twin storm killed two people, including a five-year-old girl, and flattened much of the town on June 16. Nebraska Governor Dave Heineman has called a state of emergency.

National Oceanic and Atmospheric Administration storm analyst Greg Carbin says double tornadoes occur in the US every 10-15 years.

The two tornadoes struck 1.6km apart, causing winds of up to 265kmh, according to the National Weather Service (NWS).

NWS meteorologist Barbara Mayes says the Nebraska twin tornado was unusual in that both systems were of equal strength, but it was “by no means” unprecedented.

Officials estimate 75% of Pilger – a town of 350 people – was destroyed, but no cost estimates have yet emerged.