WASHINGTON — Postmaster General Patrick Donahoe said Thursday his agency is in “the midst of a financial disaster” and may need an emergency increase in postage rates to keep operating.

“The Postal Service as it exists today is financially unsustainable,” he told the Senate Homeland Security and Governmental Affairs Committee. It’s a message that the postmaster general has been delivering to Congress with regularity over the past several months.

Donahoe pressed lawmakers Thursday for swift action on legislation to fix his agency’s finances. Without help from Congress, the agency expects its multibillion-dollar annual losses to worsen. He warned that the agency’s cash liquidity remains dangerously low.