U.K. blood banks are turning away some prospective donors after an “overwhelming” outpouring of donation interest in the wake of Monday’s deadly terrorist attack in Manchester.

Mike Stredder, director of blood donation at the U.K.’s National Health Service Blood and Transplant, said Tuesday that the organization had already collected all the blood required for hospital patients.

“We’ve had an overwhelming response from the public,” Stredder said in a statement. “We thank them for thinking of giving blood.”

In response to last night's tragic incident in #Manchester - we have all the blood required for hospital patients at the present time. pic.twitter.com/EWNAKH5mrO — GiveBlood NHS ❤ (@GiveBloodNHS) May 23, 2017

People who already have donation appointments are asked to keep them, especially if they have type O-negative blood, which can be transfused to nearly all patients. Those who don’t yet have appointments are encouraged to register with the NHS Blood and Transport database and become a future donor.

Manchester community members flooded local blood banks following one the country’s most devastating terrorist attacks in more than a decade. An apparent suicide bomber detonated an improvised explosive device around 10:30 p.m. local time at the Manchester Arena, where U.S. pop star Ariana Grande had just finished performing. At least 23 people, including the assailant, have been killed and at least 59 others wounded.

Meg Morgan, a 20-year-old student at the University of Manchester, told HuffPost she was “very saddened” by the bombing and hoped to give blood at a local donation center on Tuesday, but was told by staff that the line to donate was already out the door. She was encouraged to make an appointment or come back at another time.

“The blood bank only turned me away because there were literally too many people,” Morgan said. “Manchester has a strong sense of identity as a city, and I feel like everyone wants to find a way to help.”