The global silver-coin market is in the grips of an unprecedented supply squeeze, forcing some mints to ration sales and step up overtime while sending U.S. buyers racing abroad to fulfill a sudden surge in demand.

In his 35 years of dealing precious metals, Roy Friedman, vice president of sales and trading at Manfra, Tordella & Brookes, one of the biggest U.S. wholesale coin dealers, said he could not recall seeing a squeeze in supplies of North American silver coins spilling over to coins made in Austria and the U.K. to the degree seen this year.