Frogmore Paper Mill says a "significant amount of irreplaceable historical artefacts" have been lost in a fire.

The visitor centre at the historic mill in Apsley was "extensively damaged" on January 22 due to a fire that police say had been started deliberately in the area.

Staff and volunteers at the mill have spent the week assessing the destruction and believe the centre is "damaged beyond repair".

In an update issued on its Facebook page, Frogmore Paper Mill said: "It has been a challenging week for everyone at Frogmore Paper Mill following the fire on our site last weekend.

"Our staff and volunteers have been hard at work assessing the damage and working to salvage our collection. Unfortunately, the area most affected was our gallery and exhibition area, meaning a significant amount of irreplaceable historical artefacts have been lost."

Watford Observer: Credit: TwitterCredit: Twitter (Image: Harpenden Fire Station)

Work to save items began on the night of the fire, guided by fire crews, and Frogmore say this includes the 1624 bill of sale from Nash Mills, which has now been sent off to be assessed and hopefully restored.

This salvation work is ongoing but Frogmore admitted: "Unfortunately, it is likely that our visitor centre is damaged beyond repair."

Watford Observer: Damage at the paper mill site. Credit: Harpenden Fire Station Damage at the paper mill site. Credit: Harpenden Fire Station (Image: Harpenden Fire Station)

Those at the paper mill site added: "We’d like to again thank Hertfordshire Fire and Rescue for their extraordinary efforts in bringing the fire under control.

"Without their quick response, the fire may have spread further through the site. We’d also like to thank Hertfordshire Constabulary for their support and work to investigate the cause of the fire.

"Over the coming weeks and months we’ll be providing further updates on the work we’ll be carrying out. We remain committed to preserving the history of paper making in Apsley and the Gade Valley."

Thanks were also given to wellwishers from the community.

Watford Observer: Firefighters at Frogmore Paper Mill on January 22. Credit: Harpenden Fire Station Firefighters at Frogmore Paper Mill on January 22. Credit: Harpenden Fire Station

Hertfordshire Fire & Rescue says it had as many as 13 appliances on the scene after being called to Frogmore Road near Hemel Hempstead at around 3.30pm.

Related: Firefighter discusses rapid response after 'challenging' paper mill fire

Assistant chief fire officer Simon Tuhill, who oversaw the operation, described it as a "challenging fire" and praised his officers for working to ensure the flames did not spread to older parts of the site such as the mill itself.

The site is home to the oldest working mechanical paper mill in the world, with crews remaining on-site throughout the evening.

Police say it was reported the fire began in a skip before spreading to a building. A 13-year-old boy was arrested on suspicion of arson shortly after and has since been released under investigation.

There were no reports of any injuries.