A Greek defence ministry source said the migrants would stay on the transport ship until a new facility to accommodate them had been created on the mainland.

Some 500 people, many of them families with small children, have been stranded at the harbour since arriving from Turkey over the weekend.

Although the Greek vessel arrived at the port of Mytilene Wednesday morning, it was not until 4:00 pm (1600 GMT) that the first 15 migrants boarded, said an AFP photographer at the scene.

But the atmosphere at the harbour was tense as the port police and security forces tried to stop two Greek photographers and a German journalist from taking pictures, pushing them back and trying to grab their cameras.

A Greek military source said the migrants would stay on the ship, which normally had a capacity of 400, "as long as necessary".

Astrid Castelein of the UN refugee agency on Lesbos said they and other aid groups would provide matresses and bedding, as this type of vessel was not normally meant to house people.

- No asylum requests accepted -

On Tuesday evening hundreds of migrants, earlier arrivals on Lesbos who have already filed asylum requests, headed down to the harbour in a bid to get a berth on the ship as news of its impending spread.

After a few brief scuffles, police pushed them back.

In an effort to curb the influx, which began after Ankara said last week it would no longer stop refugees from entering Europe, Athens has suspended asylum procedures and reinforced its borders.

The weekend arrivals, who have not filed asylum requests, will get a place on the boat under this new regime, Fotis Garoufalias, president of the coastguard at Mytilene, told AFP.

"The instructions are to register them, without the possibility of making an asylum request, and to take them on to the boat for them to be transferred," he said. That process should be finished by the end of the day, he added.

The new arrivals have exacerbated an already combustible situation on the Greek islands in the Adriatic, off the Turkish coast.

Lesbos hosts more than 19,000 refugees and migrants, crammed into squalid conditions around a camp built to house fewer than 3,000, a legacy of the 2015 migration crisis.

Fed up with shouldering the burden of Europe's over-stretched asylum system, locals have protested against the presence of the migrants on their shores, saying they threaten safety, public health and a tourism-dependent economy.

That anger has spilled over into violence in recent days, with an extremist minority accused of leading attacks on newly arrived migrants, intimidating journalists and targeting aid workers, according to several groups based on Lesbos.

Locals are also angry about the government plans to build a new migrant centre on Lesbos and clashed with riot police last week.