SALT LAKE CITY — A slowdown in sales of party balloons isn't normally an important economic indicator, but it may be the tip of an iceberg of trouble.

A helium shortage that started in May is stretching on much longer than expected and has now been labeled a "crisis" by federal officials.

"My phone has been ringing off the hook," said Samuel Burton at the Federal Helium Reserve, operated by the U.S. Bureau of Land Management in Amarillo, Texas. He said a "scramble" is under way to maintain healthy supplies of the gas for critical uses in the military, industry, even in medicine.

The shortage is ironic because helium is the second-most common element in the Universe. On Earth, it's captured as a waste product in natural gas fields.