Vandals who killed tens of thousands of dollars-worth of exotic tropical and freshwater fish after breaking into and torching a western Sydney pet store, left behind a trail of blood and footprints at the shop

In what police believe was a targeted attack, dozens of colourful tanks were last night found smashed and the OFishal Pets building in Emu Plains covered in graffiti, before it was set alight.

One tank alone contained $10,000 worth of fish.

Tens of thousands of dollars-worth of exotic fish have been killed at the hands of vandals who smashed their tanks. (Supplied)

Police believe the vandals broke into the OFishal Pets store in Emu Plains, in western Sydney, and smashed tank after tank. (9NEWS)

The building was left covered in graffiti before it was set alight. (9NEWS)

Building manager Judith Wawszkowicz told 9News the incident has taken its toll on the family who have run the store for the past five years.

"They're in shock. They're in total shock," she said.

"It's devastating to see thousands and thousands of fish dead on the floor.

"A lot of the fish were expensive tropical fish - and there's no replacement for that type of loss."

In total, eight firetrucks and 40 firefighters were called to the pet shop on the Great Western Highway before 10pm.

"We encountered very intense and hot conditions, fairly severe smoke inside the building and intense flames," Inspector Kernin Lambert from Fire & Rescue NSW told 9News.

The family that has run the store for the past five years are said to be devastated by the attack. (9NEWS)

Eight firetrucks and 40 firefighters were called to the scene to battle the intense blaze. (9NEWS)

Detectives are appealing for help from the public after no CCTV vision was taken to identify the vandals. (9NEWS)

Detectives believe the vandals broke into the store through the building's back door, however there were no CCTV cameras on-sight to capture their identities.

A trail of blood and footprints leading from the back of the store to the street has been forensically examined by police, with authorities claiming the offender might have serious injuries from the incident.

Officers from the Nepean Police Area Command have established a crime scene and are appealing for anyone with dash cam footage from around the time of the incident to come forward.