Police are dealing with an ongoing incident at an industrial estate where doses of the Oxford-AstraZeneca vaccine are produced and stored.
North Wales Police said it was at Wrexham Industrial estate.
It said a cordon had been put in place near the Wockhardt plant and the public have been asked to keep away.
The BBC understands that a bomb disposal unit has been called to deal with a suspicious package. There are no reports of any injuries.
The Wrexham plant has the capability to produce around 300 million doses of the vaccine a year.
Wockhardt UK entered an agreement in August to help prepare the vaccine for distribution.
When the company’s contract was announced, Ravi Limaye, managing director, said: “We are immensely proud to have been selected to partner with the UK government on this project,” he said.
“We have a sophisticated sterile manufacturing facility and a highly skilled workforce.”
On Thursday Wrexham council leader Mark Pritchard said teams had worked to ensure the vaccine was not lost in the floods.
The Welsh Government said there had been “no adverse effects” on the coronavirus vaccine roll-out.