Parc y Scarlets is expected to be operational as a temporary hospital in around two weeks, providing up to 500 extra beds in the battle against coronavirus.
Work began on Monday to convert three areas of the stadium complex for medical use as the Scarlets work in partnership with the Hywel Dda University Health Board and Carmarthenshire County Council.
The Juno Moneta Arena training facility will house 252 beds, while there will also be a hospital area in the Quinnell Lounge in the South Stand and the first-floor concourse.
The beds in Llanelli are in addition to around 2,000 which are set to be installed at the Principality Stadium in Cardiff as Wales prepares itself for the peak of the pandemic.
"Things have progressed very quickly," said Scarlets general manager of rugby Jon Daniels.
"We are aiming to be close to operational within a couple of weeks. It is a big task and a big challenge, but everyone is pulling in the same direction.
"It is a contingency plan — as with everything with coronavirus, nobody knows how long it is going to last and how bad it could get. A lot depends on how vigilant we are in following the guidelines issued by the government and the NHS in terms of isolating ourselves and social distancing.
"The better we are at following those guidelines, hopefully the less need there will be for facilities such as this."
Daniels highlighted the Scarlets' role in the community and paid tribute to the work of those fighting the outbreak.
"There is a part of our community which needs to be recognised here and that is all those workers, those warriors within the NHS and other critical services in getting our society through this," he added.
"What we are doing is miniscule compared to the sacrifices that those people are making to get to work, to work long hours and get our community through this.
"It is hard work what we are doing here, but it is an absolute privilege to serve our community in any way we can."
Carmarthenshire County Council has also commissioned contractors to turn Carmarthen Leisure Centre and indoor bowls hall the Selwyn Samuel Centre into temporary bed spaces for the NHS.