SECURITY Branch officials are investigating the shooting of a Filipino seaman in international waters off Waglan Island. A branch spokesman said explanations would be sought from the New China News Agency if evidence suggested that Chinese security forces were involved in the attack on Panamanian-registered container ship Marine Peace. Senior Government sources said they feared the attack marked a violent renewal of anti-smuggling action by the mainland, which led to more than 20 ships being fired on and intercepted when leaving Hongkong last year. Marine Peace had just left Hongkong's territorial waters on its way to Taiwan at about 10 pm on Monday when it was fired on by men aboard a fishing boat. The 47-year-old seaman was hit in the back. He was in a satisfactory condition in Queen Mary Hospital last night. Deputy Regional Commander (Marine), Chief Superintendent Basil Lim Sak-yeung, said his officers would interview the man. ''We are looking into it to see if there is any incident involving Hongkong,'' he said. ''Pirate attacks in that area are very rare.''