A smugglers' tunnel linking the Hamas-controlled Gaza Strip to Egypt collapsed on Friday, nearly suffocating four Palestinians and trapping another under rubble, Egyptian and Hamas officials said. The Palestinians were trying to hollow out a recently sealed tunnel, located some 10 meters below ground, when its vulnerable sandy ceiling crumbled under its own weight, the officials said. Four of the Palestinians were freed by rescuers and are in serious condition at a Gaza hospital, said the Hamas official, who spoke on condition of anonymity because he was not authorized to talk to the media. Rescue workers on the Palestinian side were still digging down in search of the fifth smuggler, he said. The incident comes a day after a Palestinian was buried alive under another collapsed tunnel near the Egypt-Gaza border. The Hamas official accused Egyptian security forces of spraying a "long-acting poisonous gas" in the tunnel that collapsed Friday to smother smugglers. But an Egyptian border security official said this was "nonsense," adding that the mouth of the 700-meter-long tunnel was destroyed using explosives several days ago. "Most likely, the smoke that has resulted from this choked the smugglers as they tried to reopen the tunnel," the Egyptian official said, speaking under customary condition of anonymity. Hospital workers in Gaza confirmed the smugglers were being treated for gas inhalation, but could not say what kind. Palestinian smugglers have increasingly used tunnels to bring weapons and contraband goods from Egypt into Gaza since the territory was taken over by Hamas last June. Israel says anti-tank missiles, tons of explosives and thousands of rifles have reached terrorists in Gaza through this channel.