Alexandre Berceaux, an employee of CIS Catering at the desert gas complex, also told Europe 1 radio that the initial attack on the site was a surprise as the base was heavily guarded.
"There were intervals of heavy gunfire" on Thursday when Algerian forces stormed the base, he said. "There are terrorists who are dead, expatriates, locals," Berceaux said,
adding that he had been taken to another nearby site and was unaware if the operation was continuing on Friday morning.
He said the hostage-taking on Wednesday had come as a complete shock. "I heard an enormous amount of gunfire. The alarm telling us to stay where we were was going off. I didn't know if it was a drill or if it was real," he said.
"Nobody expected this. The site was protected. There were soldiers in place," he said. "I stayed hidden for nearly 40 hours in my room. I was under the bed and I put boards everywhere just in case. I had a bit of food, a bit to drink, I didn't know how long it would last."
"I think there are still people hidden."
He said he was found during Thursday's assault by men he believed to be Algerian military. "They were soldiers dressed in green. I think they were Algerian soldiers," he said. "I recognized some of my colleagues with them, otherwise I would never have emerged.
"I've heard there was a wounded person in the restaurant storeroom yesterday morning. Three Englishmen who had hidden above the dropped ceiling were found along with this wounded person, who was taken directly to hospital," the Frenchman said.
"I think there are still people hidden. They are in the process of doing a count now."
Algeria came under mounting international criticism on Friday as fears grew for dozens of foreign hostages still unaccounted for after the deadly commando raid against Islamist militants who had seized the remote In Amenas gas field in the Sahara desert.