Concern over low blood stocks led to the Welsh Blood Service using a loud speaker to appeal for donations.
Many regular donors have been unable to give blood over the past couple of weeks due to flu and sickness.
The service said some blood types had only a three-day supply in reserve while ideally there should be at least a five-day reserve.
A van with a loud speaker was used in Llantrisant, Rhondda Cynon Taf, to drum up donations on New Year's Eve.
Welsh Blood Service recruitment manager Trudi Evans said: "We've had quite poor blood donor sessions for the past two weeks with the sickness and viruses going around.
"In the past week, with specific blood types, they've been causing concern."
"If people have never donated, then there's never a better time to do it"The Welsh Blood Service supplies 16 hospitals in south and mid Wales, with hospitals in north Wales using the National Blood Service.
"We have to collect 600 individual donations each day and we hold between five and six sessions each day," said Ms Evans.
"Some sessions we collect 50 or 60 donations and some we collect 100 but at the moment we're collecting about half of that.
"You chip away at the blood stocks and eventually it runs dry."
Few people had signed up for the donation session at Llantrisant Leisure Centre so a van was driven around the area with a loud speaker reminding people about the session.
Ms Evans said the van worked with about 85 donations collected and it could be used again at future sessions.
Regular donors
The service is now urging people to attend donation sessions during the next week.
There are no sessions in Wales on New Year's Day but people can give on Friday at Christchurch in Fairwater, Cardiff, Llandaff city primary school in Cardiff, and the Welsh Blood Service's headquarters in Llantrisant.
"If our regular donors have missed a session because they've had flu or sickness, if they're fit and well now it's important they look where they can donate rather than miss their donation for six months," said Ms Evans.
"If people have never donated, then there's never a better time to do it."
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