The National Blood Centre has called for urgent, regular blood donations from the public as its stock is inadequate to meet daily demand.
The blood bank at the Thai Red Cross Society aims for 2,000 units a day but the target has been missed by 500 units, prompting the agency to launch a new campaign for donors to come forward.
The shortage forced the centre to sharply reduce its blood supply to hospitals in Bangkok and other provinces, which needed 8,000 units but received only 2,000 units.
Centre director Soisaang Phikulsod said in a statement the accumulated shortage came about because there are not enough regular donors.
An official at the centre said 60% of donors gave blood to the bank only once a year, such as on their birthday or another important day of the year.
The centre will encourage donors to make a donation every three months. A regular donation would help keep blood stocks up and prevent any future crisis.
Donations can be made at the Thai Red Cross Society on Henri Dunant road or its regional blood donation units in Chiang Mai, Nakhon Sawan, Ubon Ratchathani, Khon Kaen, Nakhon Ratchasima, Chon Buri, Ratchaburi, Songkhla, Phuket and Hua Hin.