By Chris Hogg
BBC correspondent in Hong Kong
Hong Kong's government has warned people with heart and respiratory conditions to stay indoors as smog chokes the territory for a second day.
Visibility in the territory is restricted
Poor visibility, caused by unusually high air pollution, has led to collisions involving at least eight ships in Hong Kong's waters.
Scientists blame the conditions on a typhoon lashing Japan and South Korea.
Typhoon Megi has created a weather pattern that has trapped pollutants, which have collected above Hong Kong.
A grey haze hangs over the Hong Kong skyline, blocking out the sun, and there is no wind to blow it away.
In parts of the harbour, visibility has been reduced to 2,000 metres (6562 feet), which has led to a series of collisions.
In the worst accident, a sailor fell overboard after his container ship hit a larger cargo vessel, but he was rescued by a police launch.
More than 120 passengers on a ferry were stranded on their vessel in the harbour for more than an hour after it collided with a tanker. A hole more than two metres (seven feet) wide was reportedly ripped in its side.
Scientists warn the haze will not lift before Friday when the typhoon is expected to move further north.
They say the build-up of pollutants is caused by the combination of stagnant conditions and high temperatures and there is nothing they can do.