A failed security system caused a huge backlog for delegates returning from a one-day break to start the second week of the United Nations climate change conference in Copenhagen.

More than 10,000 people were waiting to enter the convention center in two lines stretching about one kilometer long since the early hours on Monday morning.

Chen Ying, deputy director of the Sustainable Development Research Center under the Chinese Academy of Social Sciences, said she and her colleagues had still failed to enter the conference by 9 am local time despite waiting since 7 am with their day starting two hours before that.

One queue was lined with delegates, media groups and NGOs who had already registered. Another line, stretching much further, consisted of those who just arrived in Copenhagen for the conference. A special passage had been set up for UN staff as well as media members. The entrance choke came after the security screen system broke down and only got worse as participants started to arrive.

Police officers responsible for maintaining order said the conference hall could only accommodate about 15,000 people, compared to the larger number of 50,000 participants invited.

The officers urged people waiting to be patient via loudspeakers. "Take it easy," they said.

According to the organizing committee, the conference expects more than 45,000 participants, which include more than 10,000 UN working staff, 20,000-plus delegates from 192 countries, 3,400 journalists and the rest are local support, security and technical staff.