MONTPELIER, Vt. – There’s an urgent need for blood donations across New England to make up for shortages caused by a combination of demographics and bad weather, officials said.

The American Red Cross is asking people across New England to roll up their sleeves and donate, said Carol Dembeck, a spokeswoman for the New England Region of the American Red Cross.

“I really think people respond when there’s a crisis,” Dembeck said. “We need to get out the message that for people who need blood, it is a crisis. The need is every day.”

Dembeck said that some hospitals have less than a one-day supply of blood on their shelves. Ideally, hospitals will have a three- to five-day supply of blood, she said.

The New England Region of the American Red Cross is made up of Maine, New Hampshire, Vermont and Massachusetts.

Dr. James Aubuchon, the chairman of the pathology department at Dartmouth Hitchcock Medical Center in Lebanon, N.H., said Friday that he didn’t know of any cases where the lack of blood harmed a patient. But blood shortages routinely prompt hospitals to postpone elective surgery.

A big part of the current shortage is because of the aging of the population. As people get older, fewer are eligible to donate blood, yet more of them need blood.

On top of that, the bad weather during the last week could have kept Red Cross blood transports from reaching people who would have been willing to donate.

The key to overcoming the shortage is to get people out to donate.

“The perception of blood bankers is the public understands how important it is, but they don’t always have the motivation to respond today,” Aubuchon said.

The outpouring of blood donations in the aftermath of the Sept. 11 attacks on the United States were an example of how the public can be motivated to respond.