U.S. currency in circulation has experienced its largest percentage increase in over 20 years, according to data from the Federal Reserve Bank of St. Louis.

From March 11 to March 18, dollar banknotes in circulation shot up from around 1.809 trillion to 1.843 trillion, an increase of almost 2 percent, the data shows. The increase was noted Sunday by economist John Paul Koning.

The data is the first strong signal, beyond scattered anecdotes, that U.S. citizens are now withdrawing more cash than usual from banks and ATMs amid concerns over the effects of the coronavirus pandemic.

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The surge is the biggest since late 1999, when fear of a global digital systems crash caused by a rumored glitch in numerical dates – the so-called "Y2K bug" – sparked a frenzy of withdrawals and panic buying.

Based on the weekly change, the week ending Dec. 22, 1999, saw a 3.78 percent rise, while the week ending March 18, 2020, saw an increase of 1.92 percent.

Currency in circulation includes paper currency and coin held both by the public and in the vaults of depository institutions.

The increase comes as the global outbreak of the deadly coronavirus (COVID-19) continues to worsen in many nations, and with the health authorities advising social distancing measures and minimal contact with surfaces that might be contaminated with the virus.

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The pandemic has brought new attention to the idea that physical money represents the "dirtiest" form of currency exchange between two parties, driving the narrative further for digital value transfer, blockchain-based or otherwise.