The blood supply shortage in the United States has reached “crisis” level, according to the American Red Cross, which says it is the second time in its 150-year history that levels have been this low.

Factors such as wildfires and extreme heat have combined to create the current situation, Dr Courtney Lawrence, who works with the American Red Cross, told the BBC.

Supply levels fell by a quarter just last month. The crisis occurred during the summer, when the amount of blood hospitals need typically increases.

This is due to a greater number of car accidents and more people spending time outdoors, resulting in more injuries requiring blood transfusions, Lawrence said.

The American Red Cross, which is the largest blood supplier in the US, providing about 40% – is currently distributing about 3,500 more units than normal during this time of year, according to Lawrence, who added that the organization is having to draw “very, very little on our blood inventory.”

“We don’t have the ability to store blood very far in advance because blood has a finite shelf life and expires,” he said.

Donated blood must be used within 42 days because blood cells break down over time.