"Our immediate thoughts are with the individual's family, friends and colleagues at this very difficult time and we will support them in every way we can.
"Our further thoughts and support are with our colleagues and members of the emergency services who are being treated in hospital.
"One of our colleagues remains in a serious but stable condition. Nothing is more important to us than the safety of everyone working for us.
"We are working closely with the authorities to investigate how this tragic incident occurred and we will be in a position to say more once a full investigation has been concluded."
In a statement, the force added: "Other staff from Carlsberg and emergency service personnel remain at the hospital receiving treatment.
"The emergency services were called to Carlsberg at around 12.30pm today (UK time) following reports of a gas leak.
"Northamptonshire Police are working with the Health and Safety Executive to investigate the incident."
The gas leak was confined to the factory site and there is not thought to be a wider risk to members of the public.
Staff were evacuated from the site when the leak happened.
A statement from the three emergency servcies said: "Six fire pumps were called to the location to secure the site.
"There are no cordons around the property, and roads remain open, although motorists are advised to avoid the area if possible to reduce congestion."
