As logistical frustrations grow at the U.N. climate conference, organizers blame the pandemic.

Logistical complaints are mounting at the United Nations climate conference in Glasgow, where participants waiting in security lines for more than an hour were abruptly told on Wednesday afternoon that there was no room for them inside the venue.

At 12:15 p.m., conference organizers issued an alert notifying people that the 10,000-person capacity limit in the cavernous tented area where the summit is being held was close to being reached. Instead, they suggested, participants who could do so should watch the proceedings online.

It was the last straw for many attendees, especially environmentalists and delegates from developing countries who endured long journeys and logistical hurdles to get to Glasgow during the pandemic. The past few days, the conference limited the number of people allowed inside the venue from civil society groups. The online portals to watch the negotiations remotely have been faulty.

On Tuesday, conference organizers issued a letter of apology to participants for the long lines and video difficulties, saying that planning around Covid restrictions has been challenging. On Wednesday afternoon, Patricia Espinosa, the executive secretary of the U.N. climate body, asked attendees to “bear with us” as organizers grappled with the complex arrangements — which include ensuring that all those entering the venue have tested negative for the coronavirus, and enforcing controls on the number of people in meeting rooms.

“This is a unique COP in quite extraordinary times,” added Alok Sharma, the British politician who is serving as host of the conference. He said organizers are “working to fix” logistical issues but did not offer details.

They also did not address criticisms over issuing accreditation for 39,509 people to access a venue whose the capacity is limited to 10,000.

One veteran of the annual summit — known as COP26 because it is the 26th “conference of the parties” to the U.N.’s climate body — called it the “poorest planed” to date.Alexandria Villaseñor, a youth activist from the United States, called the conference a “hellscape.”

“An exclusionary, racist, ableist, classist environment directly informs the decision making process that is placed in it!” Ms. Villaseñor wrote on Twitter.

Asad Rehman, director of a coalition of labor, youth, racial justice and other groups focused on climate change, derided the “shabbiest organizing” he’s seen in 15 years of attending U.N. climate conferences. He said that some negotiators told him they had to cancel bilateral meetings because they were unable to get inside in time.

“There’s mounting anger about this issue of accessibility and inclusion, and huge, huge frustration not just from developing countries but also negotiators,” Mr. Rehman said. “It’s probably the poorest planned COP I’ve ever seen.”