The Report of the WHO-China Joint Mission published on Feb. 28 by WHO is based on 55,924 laboratory confirmed cases. The report notes that "The Joint Mission acknowledges the known challenges and biases of reporting crude CFR early in an epidemic". Here are its findings on Case Fatality Ratio, or CFR (the mortality rate):

"As of 20 February, 2,114 of the 55,924 laboratory confirmed cases have died (crude fatality ratio [CFR: 3.8%) (note: at least some of whom were identified using a case definition that included pulmonary disease).

The overall CFR varies by location and intensity of transmission (i.e. 5.8% in Wuhan vs. 0.7% in other areas in China).
Wuhan also suffers considerable air pollution.

The London fog of 1952 killed 12000 people
Respiratory problems from air pollution exacerbated by complications from the   corona virus likely account for the higher death rate in Wuhan. The quoted percentages are likely suspect and may well change
over time (probably downwards)
The WHO suggests 7 million are killed each year by air pollution.