Investigators were examining the charred remains of a fire which broke out overnight in Old Town early Monday morning.
The fire was first reported around 4:20 a.m. after people saw smoke while driving from the freeway.
Crews say the restaurant, El Patio, is a total loss.
When the fire department got to Congress Street they found a restaurant engulfed in flames. About 35 firefighters fought the flames for 40 minutes.
Officials say the fire may have started in the kitchen, however, the cause of the fire is being investigated by San Diego City Fire and CalFire.
The flames also jumped to two other buildings including the Gum Saan antiques store. The store sells items from as far as Tibet, reader Chris Galante told NBC San Diego.
The antique store sustained smoke and heat damage. It will be closed while undergoing repairs. A nearby store called Capt. Fitch's had minor damage, but has reopened.
The California State Parks department owns the buildings, which are replicas representing Old San Diego. The department will not pay to restore the buildings. The buildings' owners will be responsible for any restoration.
"Each one of these buildings are very popular," said Richard Dennison, Park Superintendent."We get a lot of tourists into the park, they're going to be closed for quite a while, while they're being reconstructed."
The rest of Old Town Park will remain open to visitors, Dennison said in a statement.
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