While, PK-3356, a Haj Flight from Jeddah to Karachi was holding at Jeddah runway 34; suddenly a person, ran from apron area around and climbed into the main landing gear bay. A Royal Saudi Airline (RSA) pilot witnessed this incident; and immediately reported the matter to ATC Tower, which after some reconfirmations and inquiries; informed PIA Captain regarding the presence of a person in his aircraft's Main Landing Gear (MLG). PIA captain reconfirmed the contents of the message from ATC. Four minutes later, ATC inquired from the Captain whether he would land back or continue. The pilot in turn requested air traffic controller for advice for which he was told to take his own decision. The pilot decided to continue to Karachi. He at no stage of 4 hrs flight informed Pakistan Air Traffic Control (ATC) Regarding the potential hazardous situation. On landing, when aircraft was searched, a frozen body was found in the left main wheel well.