At City Hall in Chicago on Wednesday, people waited as long as three hours to donate blood.
Hundreds of doctors and nurses, meanwhile, offered their services in the event they are needed in New York or Washington to care for the injured.
Across Chicago Wednesday, offers of assistance continued to pour in from those searching for a way to help victims of Tuesday's terrorist attacks.
Although the response has been overwhelming, Jessica Miller, a Red Cross spokeswoman, said donations of blood and cash are still needed.
Chicago Red Cross officials expected that Wednesday's blood donations would exceed Tuesday's 1,736 units, more than twice what is collected on a normal day.
Large cash donations to the Red Cross are coming from some of Chicago's largest companies, with Abbott Laboratories pledging $2 million to the Red Cross and AmeriCares. Bank One is offering to match up to $1 million in donations from employees, and Sears, Roebuck and Co. promised a minimum of $1 million Tuesday for the Red Cross.
For individuals wanting to donate money, the Red Cross, the Salvation Army and Catholic Charities have set up toll-free numbers, and Bank One branches and Walgreens stores are accepting donations for the Red Cross.
Meanwhile, David Martin, chief executive officer of the Society of Critical Care Medicine, said doctors, nurses and paramedics are still awaiting word on whether their services are needed.
"An hour after the disaster, people began calling in offering their assistance, and we began building a list of those willing to volunteer," Martin said.
Physicians at the disaster sites have told Martin they have enough people and basic supplies, but they need artificial skin for burn victims and blood.
Though commercial flights are grounded, medical supplies have been transported on American Lifeline Midwest, an air carrier of medical supplies and personnel. Abbott Laboratories sent 650 units of blood by ground Tuesday.
Five people from the Federal Emergency Management Agency in Chicago headed to New York to help coordinate victim assistance. Earlier Wednesday, 39 Chicago-area firefighters left to aid in the rescue effort.
FEMA spokeswoman Linda Sacia said she hasn't stopped fielding calls from people who want to leave immediately for New York and Washington to help in any way they can.
"People are saying, I've got a skill that can be used," Sacia said. "As human beings, we want to physically do something, but that is not necessarily what is needed."Copyright © 2015, Los Angeles Times