Detectives are appealing for information after thieves raided a jewellery store in Blackburn.
Officers were called around 2.30am yesterday following reports of a fire inside The Mall shopping centre.
After entering the building, police patrols and firefighters from Lancashire Fire and Rescue discovered a burglary at Chris Shan Jewellers.
Detectives believe up to eight men wearing dark clothing and balaclavas had smashed through an entrance door to the centre.
Once inside, offenders gained entry to the jewellers using a sledgehammer and crowbar, stealing an unknown quantity of jewellery.
The Church Street entrance was then set alight, before the offenders left the shopping centre through an exit near to County Hall and Exchange Street.
Det Insp Tim McDermott, of Blackburn CID, said: “We are appealing for information following the burglary of a jewellery store in The Mall, Blackburn. This was a well-planned theft involving up to eight people with their faces covered.”
He added: “CCTV footage indicates there may have been other offenders in addition to the eight who entered The Mall.
“This crime took place in the middle of Blackburn town centre and we would ask anyone with information, or who noticed suspicious activity in the area at the time of the incident, to contact police immediately.”