March 4 (Reuters) - Influential U.S. doctors' group the American Medical Association (AMA) on Monday asked the Biden Administration to make emergency funds available to physicians hurt by ongoing problems created by the hack of UnitedHealth's Change Healthcare unit.

The AMA said the cyberattack on Change, which provides healthcare billing and data systems, has led to disruptions of numerous administrative and billing processes at physician practices. They said that many practices have not been able to submit insurance claims for reimbursement since the hack was disclosed on Feb. 21.

"We urge HHS to utilize any available emergency funds and authorities to provide critical financial resources to physicians, ensuring they can continue to deliver essential healthcare services during these challenging times," AMA Chief Executive James Madara wrote in a letter to U.S. Health and Human Services Secretary Xavier Becerra.

U.S. Senator Charles Schumer has also written to the top U.S. Medicare official to ask that the Centers for Medicare & Medicaid Services (CMS) make accelerated and advanced payments available to impacted hospitals, pharmacies, and providers.

"Hospitals, pharmacies, and healthcare providers are facing an immediate - and rapidly intensifying - adverse impact on their cash flow and, ultimately, on their financial solvency," Schumer wrote to CMS Administrator Chiquita Brooks-LaSure on Friday.

The Change hack was perpetrated by hackers who identified themselves as the "Blackcat" ransomware group. Change said last week it had enabled a new version of its ePrescribing service for all its customers, more than a week after it reported a hack that had a knock-on effect on players across the U.S. healthcare system.

(Reporting by Michael Erman Editing by Bill Berkrot)