GENEVA, Sept. 21 (Xinhua) -- The number of refugee and migrant children who arrived on the Greek Islands between January and August jumped by 32 percent compared with the same time period last year, the United Nations Children's Fund (UNICEF) said Friday.

More than 7,000 children, averaging more than 850 each month, have arrived by sea on the Greek Islands, with most ending in overcrowded and unsafe facilities, UNICEF's country coordinator for the refugee and migrant response in Greece, Lucio Melandri, said at a UN briefing here.

"We predict the number of arrivals coming by sea will rise in the coming months," said Melandri.

He said, "As the number of refugee and migrant children arriving on the Greek Islands increases, conditions at the centers hosting these children are becoming more dire and dangerous."

Melandri said that Greek authorities and communities have done as much as they can to support refugee and migrant children, "but they can no longer cope with the sheer numbers and needs."

He said that all refugees and migrants living in the reception and identification centers, especially children, need to be transferred to the mainland without further delay.

This is to make sure they can have adequate accommodation, protection, health care and other basic services.

About 80 percent of the 20,500 refugees and migrants now on the Greek Islands, including more than 5,000 children, are being sheltered in unsanitary, overfilled reception and identification centers, said UNICEF.

Under Greek law, refugees and migrants should spend a maximum of 25 days at the centers to complete arrival procedures.

Children face health and protection risks including severe psychological distress, said Melandri.

"Violence, domestic abuse, protests and unrest are daily occurrences. Access to basic sanitation and hygiene is inadequate. In some instances, 70 people rely on one toilet," said Melandri.

Despite tremendous goodwill and commitment, the overwhelmed staff and local authorities have not been able to refer all vulnerable children and families to appropriate services, said the UNICEF representative.

"Greece cannot manage this alone," said Melandri.