Hong Kong held a nuclear emergency drill on Thursday involving over 1,000 officials and foreign experts, the city's first exercise since the Fukushima nuclear disaster in Japan last year.
The drill was meant to test contingency plans for a nuclear incident at Daya Bay power plant in China's Guangdong province, 20 kilometres (12 miles) from Hong Kong's border and 50 kilometres from the centre of the financial hub.
"This will better prepare Hong Kong to deal with any emergencies," Security Minister Ambrose Lee told reporters, describing the exercise as "successful".
Lee said experts from France, Britain and the International Atomic Energy Agency were present to observe the exercise. Some 100 residents of an island near Daya Bay were evacuated as part of the drill.
Greenpeace activists tried to participate in the exercise and managed to unfurl a banner reading "Save our home from nuclear risks" before they were turned back by the authorities.
"They have taken the easy way out -- evading nuclear crisis management and replacing it with nuclear propaganda," Greenpeace Senior Campaigner Prentice Koo said in a statement.
The two-day drill, which will continue on Friday, was announced last year shortly after the Fukushima plant in Japan was hit by meltdowns and explosions triggered by a massive earthquake and tsunami.
Tens of thousands of people were evacuated from their homes around the plant and swathes of the area remain badly polluted. Some towns could be uninhabitable for decades.
The twin power stations at Daya Bay provide most of Hong Kong's electricity.