President Xi Jinping urged China to “spare no effort” to contain the coronavirus outbreak in Beijing, as he used a conference call with tens of thousands of officials to highlight the risk to the government.

Xi issued his warning in a conference call Sunday attended by more than 170,000 government and ruling party officials the biggest of its kind according to state media. It was the second time in three days that the president and Communist Party chief had highlighted the outbreak danger near the heart of the government.

Xi’s remarks came as part of an extensive briefing on the government’s efforts to fight the outbreak, which he described as the most difficult such episode since the Communist Party came to power 70 years ago. He urged officials to work to the best of their ability to cut off sources of infection and prevent and control the epidemic.

The warning comes days after Beijing’s West District home to central party and government compound Zhongnanhai quarantined 69 people who had close contact with a local government official who tested positive for the virus. Beijing had reported 399 cases of the disease and four deaths as of Sunday, according to the World Health Organization, the 12th most among China’s more than 30 regions.

The Standing Committee of the National People’s Congress is expected Monday to consider a proposal to postpone the start of parliamentary meetings planned to begin next week. On Friday, Xi told the party’s 25-member Politburo, which includes Beijing party chief Cai Qi, that municipal authorities in the capital must “do a good job” containing the virus.