BEIJING - China's maritime authority on Friday ordered a cease on all production operations on the leaking Penglai 19-3 oil field in China's Bohai Bay that is being developed by ConocoPhillips China (COPC).

The State Oceanic Administration (SOA) said in a statement that COPC failed to meet the SOA's requirements of "screening out all potential sources for oil spills and blocking leaks once and for all."

The company on Wednesday submitted a report to the SOA claiming that the two goals had been met.

The SOA began its verification of the report Thursday, employing satellites, airplanes, ships and underwater robots to evaluate the clean-up work.

The SOA determined that "the oil on the seabed near platform C has yet to be completely cleaned and small amounts of oil are still leaking from the seabed. The oil collection measures adopted on platform B can not tackle the root cause of the spill," according to the SOA's statement.

Grey and black slicks could still be spotted on the water's surface about 500 meters away from platform C, according to Xinhua reporters at the scene.

"If slicks are black, it means that the slick is very thick," said Zhou Qing of the SOA's North China Sea.

Henry, the COPC's oil field manager who only gave his first name, said in a phone interview that the slicks were present was because clean-up efforts were hampered by wind gusts on August 28 and 29.

However, the existence of lingering slicks begs the question, "Has ConocoPhillips really blocked all the oil spill sources?" said Lin Fangzhong, deputy head of the North China Sea branch of China's marine environment monitoring fleet under the SOA.

When asked whether there is a timetable for the final clean-up, Henry said there is no such timetable as many unknown variables still exist.

ConocoPhillips China, a subsidiary of US energy giant ConocoPhillips, first reported spills to authorities in June. The oil spills have spread to beaches in Hebei and Liaoning provinces. The spills have been blamed for losses in the provinces' tourism and aquatic farming industries.