In photos, it's hard to make out Hong Kong through the thick, gray haze.
Smog, made worse by winter weather conditions and wind, has blanketed the city. The coastal skyline is barely visible, and ships in the region's busy harbor appear veiled like ghosts.
According to World Air Quality Index, the city is experiencing unhealthy levels of air pollution. This assessment is based on hourly measurements of pollutants like particulate matter and carbon.
Studies of particulate matter show exposure causes serious health conditions like heart and lung disease. When inhaled, the small particles are lodged in lungs and can enter the bloodstream.
Conditions aren't expected to significantly improve until later in the week, but sensitive groups like those with chronic conditions or the elderly may still be at risk of respiratory issues.
According to reporting by news agency AFP, residents that venture outside are finding the air difficult to breathe in.
This week's conditions are a reminder of how far the country still has to go to improve its historically bad air pollution.
In Hong Kong, a clean air plan was put in place in 2013 to tackle the three biggest contributors to the city's bad air: power plants, marine vessels, and motor vehicles.
Street-level pollution from diesel vehicles has been a particularly pervasive health issue for the more than seven million people that live in Hong Kong.
A 2016 plan to address street-level pollution has been effective in reducing roadside air pollutants, according to the Hong Kong government's environmental agency website.
It wasn't until the 1980s that the region was besieged by air pollution because of rapid urbanization and industrialization.
Despite environmental improvements in the city, Hong Kong is still highly susceptible to weather conditions like sea breezes that can trap pollutions, especially during winter.
Only five years ago, China implemented their National Air Quality Action Plan billed as a "war on pollution."
In a report released by Greenpeace earlier this month, the environmental watchdog group found the legislation drove a "dramatic improvement in air quality" in eastern China. However, in some coastal areas, a revamped push for coal in 2016 has threatened to reverse gains made by the plan.