By Elinda Labropoulou, Chris Liakos, Stephanie Halasz and Tamara Qiblawi, CNN

(CNN) -- Europe's largest migrant camp, Moria, has been devastated by massive fires that broke out early Wednesday at the overcrowded site on Greece's Lesbos island.

Greek authorities believe that the fires were started by Moria camp residents expressing "dissatisfaction" with coronavirus-related lockdown measures. The camp has been under lockdown after 35 people tested positive for Covid-19 earlier this week.

The refugee camp is home to an estimated 13,000 people, more than six times its maximum capacity of 2,200 people. More than 4,000 children, including 407 unaccompanied minors, live in the camp, according to the United Nations Refugee Agency.

In a televised statement, Greek Prime Minister Kyriakos Mitsotakis declared a state of emergency on the island, condemning the rioters who started the fires.

"I recognize the difficult conditions. However, nothing can become an alibi for violent reactions to health checks. And, much more, for riots of this magnitude," said Mitsotakis. "The situation in Moria cannot continue because it is a matter of public health, humanity and national security at the same time."

There are no reports of injuries, but George Moutafis, a photographer on the ground, told Greek TV channel Mega the camp had been "completely destroyed."

"The Moria camp no longer exists. The camp has been completely destroyed. The containers and tents have been completely destroyed. The fires are now out. Many migrants and refugees are now back at the camp and looking for their belongings," Moutafis said. Charity and activist groups on the ground also say that the fire has destroyed large swathes of the camp.

"Last night some people living in the camp were angry about the quarantine. They started a small fire. So police came and there was tear gas. And then the fire grew and we had to run," said a camp resident, who declined to disclose his full name for security reasons.

"All the camp is burned. There is nothing there. I am standing out on the street, near the camp, there are many people here. There is also police but they don't tell us where to go," said the resident. "We have no food or water. They say 'wait here.' It is very hot today and there are women and babies."

Congolese camp resident Paul Kadima Muzangueno told CNN that a group of minors started the fire.

"They started fires everywhere," said Muzangueno. "Everything deteriorated quickly. The police did not contain the situation."

"In the evening, the anger and despair of the refugees who have been interned at Moria erupted," the German charity group Mission Lifeline said in a statement.

"First there was a dispute at the Covid19 station in the camp which spread to the entire area during the night. Security forces used tear gas," the statement said. "A large part of the dwellings burned down. The homeless people fled into the surrounding olive groves."

Axel Steier, Co-founder of Mission Life, said he warned that the situation would "escalate" over the camp's poor conditions, calling the lockdown measures "the final straw."

"The people in Moria are exposed to extreme psychological stress. The lockdown of the camp has now been the final straw," said Steier. "The refugees in Moria are not treated as humans.

"Among other things, we asked the (German) federal government again and again to evacuate all people from the Greek camps. But hardly anything has happened," Steier added.

The Moria encampment extends out of the main UN camp into olive groves where thousands live in makeshift wooden huts they built out of wooden pellets and tarpaulin, hammered down with nails. The inhabitants say they wait for hours to use a bathroom, and sometimes spend an entire day queuing for food.

When CNN reported from the camp in March, a rank odor filled the air, the river was strewn in garbage and camp dwellers staged protests at the island's main port on a nearly daily basis demanding transport to the Greek mainland.

On Wednesday, migrant residents of Moria described being in a state of limbo, waiting for instructions from authorities among their charred belongings. "We have been told nothing. No one has shown up," said Muzangueno. "We are here and we are waiting."

Mitsotakis has promised to house the migrants in "suitable tents" but said they would be banned from traveling from the island.

In a statement Wednesday, the United Nations refugee agency says they have deployed staff to the ground and offered assistance to Greek authorities.

"UNHCR, the UN Refugee Agency, deplores the fire that largely destroyed Moria's Registration and Identification Center (RIC) last night and thanks to the local authorities, including the fire department and emergency services that helped to contain the fire and assisted the people," the statement said.

German Foreign Minister Heiko Maas has called the fire that ravaged Moria a "humanitarian catastrophe."

"What is happening in Moria is a humanitarian catastrophe," tweeted Maas. "As quickly as possible, we have to clarify with the EU commission and other EU countries willing to help, how we can support Greece. This includes the distribution of those fleeing amongst those in the EU willing to accept them."