Jas Upaul, 60, and his 59-year-old wife Rani were also bound with cable ties during the raid.
The pair were asleep when three men wearing balaclavas entered their home in Highcross Road by forcing the back patio doors with a paving slab.
The offenders then got in to the bedroom and assaulted the couple. Before leaving, the three men broke into a safe and stole jewellery, cash and personal items.
Both victims were taken to hospital, with the husband suffering a broken jaw, fractured eye socket, severe swelling and bruising.
"We are pursuing a number of lines of inquiry but would very much like to hear from anyone who may have information about the robbery..." - DC Alan Poulton
He has since undergone surgery to treat some of his injuries.
His wife also suffered a fractured eye socket as well as other injuries.
Mr Upaul said: "We went up to bed just before 10pm and the next thing I knew was hearing them come up the stairs.
"The three of them were standing in the entrance to our bedroom. They said 'where's the safe?' and before I could say anything I was hit and landed on the floor.
"I fell to the ground and they kicked me and then they punched me in the face and broke my jaw.
"I said 'don't hurt my wife' because out of the corner of my eye I could see them taking her necklace off.
"They didn't even give me any time to say where the safe was before they attacked me."
DC Alan Poulton said: "This was a violent robbery by offenders who knew what they wanted.
"This was an isolated incident, albeit an incredibly frightening one for the gentleman and his wife, who were asleep when these men forced their way into their home.
"We are pursuing a number of lines of inquiry but would very much like to hear from anyone who may have information about the robbery.
"If you saw anyone acting suspiciously in the area at the time of the offence or have been offered unique jewellery recently at discounted prices, we want to hear from you as soon as possible."
A cash reward of up to £5,000 is offered to anyone who provides information which directly leads to the arrest and conviction of any person responsible for this crime.
Anyone with information about the attack, which happened at around 10.15pm on Tuesday, July 1 should phone DC Poulton on 01474 330600 or Crimestoppers, anonymously, on 0800 555111.
Don't miss out, subscribe today. Keep up to date with our newsletters.
A guide for your future. For year 11 students in Kent and Medway. Click here for the e-edition.
Education, Training & Childcare is a special supplement published by KM Media Group four times a year. Click here for latest e-edition.
Get the latest food and drink news, recipes from some of the nation's top chefs plus updates from Kent's vineyards and breweries.
Search in your local area to find your perfect partner in Kent, with FreshStart Dating! PLUS, register for free!.
Find out what's going on in the garden, with Kent expert Lucy Hewett's weekly update.
Buy pictures that you've seen in a KM newspaper, or send in a picture and we will place it on our photo sales website so that you can purchase a super, unique gift.