By Martin Sadongdong A Chinese survey ship which was earlier tracked to have been operating within the country's exclusive economic zone (EEZ) has re-entered our territorial waters without informing authorities in an apparent defiance to President Duterte's order. Defense Secretary Delfin Lorenzana said Friday that the re-entry of Chinese oceanographic survey ship "Zhangjian" within the country's EEZ was just "okay" as long as they will not stay there for too long. "Actually, I have seen the movement of that survey ship and most of his movements were outside our EEZ, in the Pacific Ocean, but sometimes it was entering our EEZ. Probably it was doing some surveys or just avoiding big waves or bad weather. I think it's okay, just don't stay within our EEZ for too long," he said. The presence of Zhangjian was revealed in a satellite image provided by Ryan Martinson, assistant professor of Chinese Maritime Studies Institute at the US Naval War College, on his social media account on Thursday. He said Zhangjian has re-entered the Philippines EEZ heading towards west at 190 knots. https://twitter.com/rdmartinson88/status/1164209907865968640 Martinson was the one who also disclosed Zhangjian's first sighting last August 6 about 80 nautical miles off the country's east coast. Earlier this week, Presidential spokesperson Salvador Panelo said the President had issued a warning to all foreign vessels that they must seek a clearance from concerned authorities first before passing through the country's territorial waters. READ MORE: Foreign vessels passing PH’s waters must get gov’t clearance – Palace Panelo added that they must comply with the order in a friendly manner or the government will enforce it in an "unfriendly manner." Lorenzana admitted that Zhanjian did not coordinate with any military unit in the area as it made a brief pass. "Wala (None)," the Defense Chief replied when asked by reporters if Zhanjian had informed the government about its brief passage. According to Senior Associate Justice Antonio Carpio, foreign vessels are not required to seek prior permission or notification when passing through a coastal state's territorial sea or archipelagic waters under the United Nations Convention on the Law of the Sea (UNCLOS). However, it was also stated in Article 40 of UNCLOS that foreign ships, including marine scientific research and hydrographic survey ships, "may not carry out any research or survey activities without the prior authorization of the States bordering straits" during a transit passage. "We will see what we can do. Huwag muna tayong mag-ano ngayon ng plano. Pag-aralan muna natin (Let us not make a move now. Let us study this case first.) We will get experts to interpret the UNCLOS," Lorenzana said.