Nobody was hurt, but hundreds of firefighters battled flames for more than 15 hours, and state media said about 1476 tons of oil had spilled into the sea, causing a 71 square mile slick.
The clean-up operation may take five days, officials said.
Industry sources are divided on how long the port will stay shut, with some estimating between seven and more than 10 days, but officials could not give a timeframe.
"The port was sealed right after the explosion. We have a one-week contingency plan, but are hoping that the oil spill can be cleaned up as soon as possible," an oil executive told Reuters.
The incident drew the attention of top Chinese officials, including President Hu Jintao, Premier Wen Jiabao and security chief Zhou Yongkang, who all issued statements and instructions during the blaze. But port officials did not show up at a news conference on Monday morning, a city government official said.
Workers are using skimmers and dispersants to break up the oil slick and stop it spreading, the official China Daily said. The pollution is concentrated about 62 miles offshore.
It's small potatoes compared to the BP Deepwater Horizon disaster in the Gulf of Mexico (where the new cap and tests appear to show some problems with seepage from the vicinity of the wellhead), but China's environmental disasters add up because of the sheer numbers of problems with China's lax environmental protections.
Last week, it became public that there was a major spill toxic chemicals from a copper plant that led to an outcry only after the spill reached a major river. The largest gold producer in China, which owns the copper plant, didn't disclose the leak for nine days. That was due in part to heavy rains damaging a plastic liner, but an illegal drain enabled the runoff to hit the Ting River. The company claimed that the heavy rains were responsible, but the company's conduct shows a disregard for environmental concerns.