Canadian Blood Services has announced the country is facing a "concerning" shortage of blood due to fewer donations this summer and a constant demand from hospitals.

The not-for-profit organization said more than 50,000 donations are needed between now and Labour Day to keep blood inventories at "an acceptable level."

As a result, the group has extended its Blood Signal rally until September 3, extended hours at its existing clinics and is adding special clinics in selected locations.

Susan Matsumoto, the executive director of Donor and Clinic Services, said every summer is a challenge, but the trend is especially concerning this year.

Due to the blood shortage, she said the group is currently drawing on its national reserves.

Canadian Blood Services — which manages the national supply of blood and blood products — operates 42 permanent collection sites and more than 20,000 donor clinics across the country.