"We were there all night doing stand-bys and ensuring that the fire was extinguished. Our fire investigator is returning this morning at 8 o'clock. At this stage, there's no indication of what caused the fire."
The building was about 300 square metres, he said.
The upset operator of Greerton Produce said this morning he received a call at about 1.30am from the Fire Service.
"I got there in about ten minutes."
He said he wasn't sure when he'd be back in business.
"I had a look at the damage it has done...very extensive damage. Most of the stock has smoke damage or water damage."
He said firefighters told him the fire possibly started in an area containing a computer and power sockets in a back office but this was unconfirmed.
The grocer hoped to be back open soon but said the building ceiling was badly damaged.
An SNPA photographer saw firefighters outside Greerton Produce, as smoke billowed out of the building just after midnight.