Media playback is unsupported on your device Media caption James Reynolds spoke to migrants as they arrived on the Greek island of Kos

The refugee crisis on the Greek islands of Kos, Chios and Lesbos is "total chaos", the UN refugee agency UNHCR says, with inadequate accommodation, water and sanitation.

Around 50,000 people arrived in Greece in July alone, the organisation says.

Greece's leader said the country was unable to cope, and called for EU help.

Separately, Italian police arrested five suspected traffickers over the deaths of about 200 people after a migrant boat sank on Wednesday.

They included two Libyans, two Algerians and a Tunisian, held on suspicion of multiple murder and people trafficking.

Survivors have said that traffickers used knives to slash the heads of African migrants and belts to thrash Arabs to keep them in the hull.

In other developments:

Some 380 people rescued from a fishing boat were brought to Sicily, a day after being rescued

The UNHCR strongly criticised the British and French governments over the situation in Calais, where 3,000 migrants are living in makeshift camps, saying it should be treated as a "civil emergency"

A Sudanese national has been charged after allegedly walking nearly the full 50.5 km (31-mile) length of the Channel Tunnel towards the UK

Austrian authorities have stopped taking any more migrants at the country's main reception camp in Traiskirchen

Image copyright AP Image caption These migrants were among 381 rescued by the Italian Coastguard ship Fiorillo and brought to Sicily

Image copyright AP Image caption The migrants were on board a fishing vessel which was in trouble off the Libyan coast

Image copyright AP Image caption Ali Rouibah (centre) is one of the five alleged people traffickers being held by Italian police

The UNHCR says nearly all new arrivals in Greece are refugees from the wars in Syria, Iraq and Afghanistan.

The organisation's European Director, Vincent Cochetel, said facilities for the refugees on the Greek islands were "totally inadequate", after more migrants arrived in Greece in July 2015 than in the whole of the previous year.

Greece's EU partners must do more to ease the burden, he said, but Greece must "lead and co-ordinate".

"On most of the islands there is no reception capacity, people are not sleeping under any form of roof. So it's total chaos on the islands.

"After a couple of days they are transferred to Athens, there is nothing waiting for them in Athens," he complained.

Greek Prime Minister Alexis Tsipras said the problem "surpasses" Greece's abilities, and that his country's economic problems meant it was facing a humanitarian "crisis within a crisis".

Media playback is unsupported on your device Media caption Greek Prime Minister Alexis Tsipras: "Now we will find out whether solidarity in Europe is real"

Image copyright Reuters Image caption Syrian Mustafa Mohammad and this young boy came ashore on Lesbos on Thursday

Save the Children says refugee children are at risk of exploitation and disease in Greece because of the lack of facilities.

"The risk to a child forced to sleep on the street of being abused, or of a baby dying of heatstroke, is very real," said Kitty Arie from the charity.

"This is Europe in 2015. We can't leave these children in this desperate situation."

Image copyright AP Image caption Lesbos is seeing an influx of Syrians and Afghans like these people helped ashore from a dinghy

Separately, another UNHCR official described conditions at Austria's main reception camp, 20km (12 miles) south of Vienna, as "intolerable, dangerous and inhumane".

About 4,500 people are at the camp, which was built to house 1,800. Many are now sleeping in the open.

Most arrived in Austria via neighbouring Hungary - both EU member states and both in the border-free Schengen zone, where passports are generally not checked.

Image copyright AFP Image caption Traiskirchen, Austria: Many migrants are sleeping rough as the main reception camp is overcrowded

EU border agency Frontex says it has not received enough pledges of assets from EU states to help Greece and Hungary with the current influx of migrants.

Meanwhile, the EU is struggling to cope with the thousands of migrants heading for Italy aboard unseaworthy vessels from Libya, where people traffickers are charging huge sums to smuggle them into Europe.

On Thursday, Irish navy ship LÉ Niamh docked in Sicily with 367 migrants - mostly Syrians - who were rescued from Wednesday's sinking.