The theft of 600 cartons of meat from Zammit Ham and Bacon curers at Pendle Hill has puzzled police, who have few leads as to the identity of the ham burglars.

The gang struck about 1.30am on Sunday, obscuring security cameras at the factory before cutting a hole in the refrigeration sheeting that formed the outer wall of the main cool room.

Once inside, the thieves used the company's electronic palette jack to move the hams to the opening. They then passed them through the hole and into a truck they had parked in a vacant adjoining block.

Not content with their lucrative haul, they decided to deal the Zammits one more blow - scrawling a a cheeky "Thanks. Merry Xmass" message on an internal wall. The theft was discovered by workers about 5.30am on Sunday.

Company manager Anthony Zammit said the theft was a major blow to the family business, which was already under pressure to meet the increased Christmas demand. Mr Zammit said a 24-hour roster for his staff would likely continue seven days a week until Christmas Day to try to make up for the loss.

"This is our busiest time. We've never had anything like this before," he said. "I'm sure it has happened before but not on such a huge scale."It's about $100,000 worth of goods. It's a pretty big blow for us." The company has posted a $5000 reward for information leading to the arrest of the gang.

Australian Pork Limited said the theft, coupled with last month's fire at the Primo Smallgoods factory at Greenacre, could result in a shortage of local hams this Christmas. But a spokeswoman said there was a flood of imported hams on the market, ensuring prices would remain relatively low, adds the Daily Telegraph.

"There will still be hams at Christmas," the spokeswoman said. “The real problem is the Australian industry is downsizing and the market is being flooded with imports."

Police have seized a number of items from the Zammit factory for forensic testing.