A cordon was thrown up around the Wrexham Industrial Estate and nearby roads were closed on Wednesday.
A bomb disposal unit was sent to the warehouse, which is owned by the Indian drug-maker Wockhardt.
“Wockhardt UK in Wrexham this morning received a suspicious package. All relevant authorities were immediately notified and engaged,” said a spokeswoman from the company.
“Upon expert advice we have partially evacuated the site pending a full investigation. The safety of our employees and business continuity remains of paramount importance.”
North Wales Police asked the public to avoid the area until further notice.
Wales’ First Minister Mark Drakeford said the Government was working with local police and the military to find out more about the incident.
“Thank you to the security personnel who are on-site to protect lives and ensure the safety of our vaccine supply. This highlights the vital role they play in keeping us all safe,” said Mr Drakeford on Twitter.
Wrexham MP Sarah Atherton said she had spoken with Wockhardt UK.
“I am assured that they are doing everything to keep their employees and the businesses around them safe” said the MP on Twitter.
North Wales Police later said a team from the Royal Logistics Corp “attended and examined the package to make sure it was safe to handle”, adding that the contents would be taken away for analysis and an investigation would continue into the circumstances surrounding the incident.
Shortly before 5pm, a Wockhardt spokeswoman said that while manufacturing had been “temporarily paused”, staff were allowed back into the facility after the package was “made safe”.
She added: “This temporary suspension of manufacturing has in no way affected our production schedule and we are grateful to the authorities and experts for their swift response and resolution of the incident.”
The fill-and-finish stage of the vaccine’s production is undertaken at the facility, which was visited by Boris Johnson in November.
Speaking at the time, the Prime Minister welcomed facilities like the Wrexham plant and said they could “really be the salvation for humanity”.
Wockhardt UK previously said it has had a presence in Wrexham for over two decades and employs more than 400 people at its manufacturing facility.
Emergency teams were called out to protect supplies of the Oxford University and AstraZeneca coronavirus vaccine following flooding at a manufacturing site on Thursday.
Leader of Wrexham County Borough Mark Pritchard said that authorities worked “through the night” to ensure that the site was not overwhelmed by flood water.
— to www.standard.co.uk