Aid groups working at two large migrant camps that have sprung up in Paris called on authorities Thursday to address deteriorating conditions, which they say could lead to security and health risks.

Around 1,600 migrants, mostly from Sudan and Eritrea, have constructed makeshift shelters under an overpass in the northern Villette area -- one of the largest camps in the French capital since the surge in arrivals to Europe beginning in 2015.

An additional 600 people, mainly Afghans, are sleeping in a tent city along the Canal Saint-Martin.

"The situation is increasingly alarming," Louis Barda of Medecins du Monde (Doctors of the World) said this week, calling the Villette camp "unlike any we've ever seen in Paris".

While two doctors nearby were treating patients as others washed their clothes in the nearby canal, a young man suddenly began convulsing, AFP witnessed on a visit to the camp.

The seizures stopped a few minutes later, but the man was muttering gibberish with a panicked look on his face. He refused to go along with first responders for treatment.

"He probably took some drugs," Barda said, adding that he and his colleagues had noted "more and more addictions" at the site.

Tensions "have clearly gotten worse over the past two weeks," he said, citing people who have needed treatment "after being hit with iron bars, people with gaping wounds, knife cuts".

On Sunday a Sudanese man was seriously injured during a fight, while a young Afghan drowned in the Canal Saint-Martin last week.

Another migrant's body was also fished out of the canal near the "Millenaire" camp at La Villette.

Meanwhile volunteers are grappling with an outbreak of respiratory and skin conditions such as scabies in the squalid, tightly packed camps.

"The security and health of the people living in these camps, but also of members of aid associations and local residents, are no longer assured," according to a petition signed by more than 30 aid groups, released Thursday.

- 'Knife in the stomach' -

"I've been here about two weeks," said Ahmad at the Millenaire camp. "It's so difficult, at night it's so cold, no good food, no washing -- it's a terrible time."

"Three or two days ago I saw one person, someone hit him with a knife in the stomach," he said.

Aid groups say the camps have attracted smugglers from the port city of Calais, offering them a chance to reach Britain -- where many migrants believe it would be easier to find work and potentially asylum.

But "if you want go to England you have to pay 1,000 euros ($1,180). It's too expensive!" said Beniam, a 26-year-old Eritrean, who says he prefers France because of its "schools and jobs".

"Their days are reduced to finding food, toothpaste or soap, to washing their clothes. They're stuck in these camps and unable to imagine anything else," said Alix of the NGO Utopia 56, declining to give her full name.

"What's happening here is also because the state isn't accepting its responsibilities, so citizens and associations have to pick up the slack," she said.

Paris Mayor Anne Hidalgo has called on the government of President Emmanuel Macron to find shelter for the migrants, only to be told that unless she wants government forces to evacuate the site, the problem is hers.

The impasse has led to a series of calls for urgent action, with senior Paris priest Benoist de Sinety denouncing "a total absence of humanity".

"If you let the camp get bigger, you're leaving them exposed to smugglers," said Barda of Medecins du Monde.

"They'll do their deals and maintain the trafficking, fuelling all the tensions we're seeing today."

Tents where migrants live are seen on the Quai de Valmy of the canal Saint-Martin in ParisThomson Reuters