Residents and tourists were counting their dwindling banknotes in the wake of Hurricane Maria, which crippled the electrical grid and communications network, turning the Caribbean island into a largely cash-based economy.

The New York branch of the U.S. central bank, which oversees and makes funds available to Puerto Rico's financial institutions, said it was prepared for another surge in cash demand and could rush more banknotes to the island if necessary.

ATMs are slowly re-opening a week after Maria, the most powerful hurricane to hit Puerto Rico in 90 years, caused widespread flooding and badly damaged homes, roads and other infrastructure on the island of 3.4 million.

The New York Fed's cash distribution operations were working and it had adequate stocks to meet the needs of lenders and other firms on the U.S. territory, a spokeswoman told Reuters.

"Demand for cash is extraordinarily high right now, and will evolve as depository institutions regain power, armored car services are able to reach branches, and ATMs are once again active," the spokeswoman said.

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