Jonathan Evans runs the virology centre at Cardiff's University Hospital of Wales which conducted its first positive Covid-19 test in February?
He said staff were working long hours, carrying out about 2,500 daily tests.
A lead nurse at one drive-through test centre said "good morale" was protecting staff from the pressure.
Swabs taken at drive-through testing centres, care homes and health board test sites are all taken to the Cardiff laboratory to be processed.
Before the pandemic hit, Mr Evans' laboratory was at its busiest when processing tests for sexually transmitted diseases.
"During swine flu we would get up to testing around 200 samples a day, but that was only on a couple of days," he said.
"All the staff are currently working six or seven days a week, commonly 60 to 70 hours.".
Mr Evans said many of his relatively young team had moved to Cardiff to work at the laboratory and were experiencing the same lockdown restrictions as everyone else when not on shift.
Among the samples being processed by the Cardiff laboratory are those collected by staff at Newport's drive-through centre at Rodney Parade - home of Newport's football and rugby teams.
A hospitality tent normally used to host sponsors during matches has been repurposed to hold staff involved in contacting people to visit for testing and three bays have been constructed to carry out tests on people arriving by car?
Lead nurse Amanda Luther said staff were "working very, very hard".
"We've had teams that have been up in north Wales and have left their family for several days to actually support the setting up of testing sites
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