A Syrian refugee is in critical condition after what appeared to be a self-immolation attempt on the Greek island of Chios, according to medical sources.

The incident happened around 2pm local time (11:00 GMT) on Thursday inside the Vial detention centre.

Videos posted on social media showed the 29-year-old man - who was holding what looked like a fuel container and a lighter - being engulfed by flames, just moments after a tussle with a police officer who had grabbed him from behind in an apparent bid to stop him from setting himself on fire.

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The refugee, who reportedly arrived on Chios last week, sustained burns to 85 percent of his body. He was initially admitted to the island's Skilitseion Hospital and was expected to be air lifted to the capital, Athens, for further treatment.

"His condition is particularly serious, and that is why all procedures have been followed to transfer him to Athens with the first available means," Eleni Voutierou, the hospital's acting manager, told Al Jazeera.

The police officer was also injured in the incident, suffering burns on seven percent of his hands and three percent of his face. He was also expected to be transported to an Athens hospital.

Delays and despair

The incident comes three days after the apparent suicide of another Syrian refugee in the Greek port of Piraeus, near Athens.

The Greek coastguard on Thursday confirmed to Al Jazeera that the man who had been found hanged on Monday close to a passenger ferry terminal at Greece's biggest port had been identified as a 25-year-old Syrian.

An estimated 62,000 refugees and migrants are currently stranded in mainland Greece and its islands following a wave of European border closures and a controversial deal between the European Union and Turkey in March last year.

READ MORE: Number of Syrian refugees surges in 2017

Under the agreement, migrants and refugees arriving in Greece after March 20, 2016, were to be held in centres on five islands, including Chios, and deported to Turkey if their asylum applications are rejected.

Since then, tensions across Greece have often boiled over as the relocation process moves slowly, is applied inconsistently, and is fraught with particular difficulties, including refugees having to navigate a complex legal asylum system in foreign languages.

Amid the difficult living conditions, the delays and the despair, some attempt to kill themselves and many self-harm, according to rights groups.

"Many asylum seekers and migrants stranded in Greece, and trapped on the islands, have seen their mental health deteriorate due to the conditions in which they live in, and the climate of insecurity about what will happen to them in the future," Eva Cosse, Greece specialist at Human Rights Watch, told Al Jazeera.

READ MORE: Refugees attempt suicide by hanging from tree in Greece

Rights groups are also warning that despite large amounts of funds being made available, refugees are still lacking access to much-needed mental healthcare and psychosocial support.

"The authorities should transfer people as fast as possible to decent accommodation on the mainland, and improve provisions for much-needed mental health services and psychosocial support. The European Commission should also ensure that the allocated aid benefits all refugees without discrimination, including people with psychosocial disabilities," Cosse said.

Aid agencies and humanitarian workers have long warned of a worrying level of mental health issues, including self harm and depression, among uprooted asylum seekers, particularly in unaccompanied ones, who have risked everything to find a better future.

"Many refugees come from Afghanistan, Iraq and Syria, and have survived human rights abuses, torture or witnessed war crimes which can be traumatising," Roland Schoenbauer, spokesman for the United Nations' refugee agency in Greece, told Al Jazeera.

READ MORE: Greece charges cleric with child refugees' sexual abuse

"Many, including some of the economic migrants, arrived in Greece with a dream which has been disrupted in the meantime. Long waiting periods for clarity, for reunion with painfully missed relatives in other European countries, or for relocation have made many people desperate, particularly in those government-run camps that could not be brought up to standard."

His comments were also echoed by Kuriakos Katsadoros, a psychiatrist with Klimaka, a suicide prevention non-governmental organisation that runs a helpline in Greece.

"Under these conditions, tense situations could lead to such unfortunate incidents [including attempted suicides]," said Katsadoros, the scientific director of Klimaka's Greek Suicide Prevention Centre.

"And amid such large numbers, there are people who are vulnerable and in need of help - which they often can't find, unfortunately, in Greece," he told Al Jazeera. "They need support, not only from the strained Greek authorities but also from Europe."