A nine-day quarantine imposed on parts of a northern Chinese city where a man died of bubonic plague has been lifted, China's official news agency reported Thursday.

A total of 151 people were under observation in the city of Yumen in Gansu province after authorities determined they had come in contact with a man who died of the plague July 16, the Xinhua News Agency reported. It said none of them had reported symptoms of the disease.

Investigators believe the 38-year-old man contracted the bacterial infection after contact with a marmot, Xinhua said. During the quarantine, authorities in the city of about 180,000 carried out disinfection and rat extermination, according to Xinhua.

Bubonic plague killed millions of people in Europe in the 14th century and tens of thousands in China in the 19th century. It remains endemic in northwest China and is spread largely through flea bites. The bacteria can cause gangrene, seizures and fever.