A video blogger in the city of Wuhan who had been documenting conditions at overcrowded hospitals at the heart of the outbreak has disappeared, raising concerns among his supporters that he may have been detained by the authorities.The blogger, Fang Bin, is the second citizen journalist in the city to have gone missing in a week after criticizing the government’s response to the coronavirus epidemic.Mr. Fang began posting videos from hospitals in Wuhan on YouTube last month, including one that showed a pile of body bags in a minibus. In early February, Mr. Fang said he had been briefly detained and questioned. A few days later, he filmed an exchange he had with strangers who showed up at his apartment claiming to bring him food.Mr. Fang’s last video, posted on Sunday, was a message written on a piece of paper: “All citizens resist, hand power back to the people.”Last week, Chen Qiushi, a citizen-journalist and lawyer in Wuhan who recorded the plight of patients and the shortage of hospital supplies, vanished, according to his friends.