Greece has sent a cruise liner and extra riot police to the resort island of Kos as tensions mount over an influx of migrants and refugees.

Greek minister of state Alekos Flabouraris said a ship with a capacity for at least 2,500 people was dispatched to Kos, which has seen a spike in refugees in recent weeks.

The cruise liner was converted into a reception centre to process arrivals and would dock in the main port of the island, the minister said.

Two riot police units were dispatched to Kos from Athens and police reinforcements from nearby islands were also drafted in, police said.

The extra police deployment came after the island’s mayor, Giorgos Kiritsis, warned of “bloodshed” if the situation on the island of 33,000 people – where around 7,000 migrants are waiting to apply for immigration papers – worsened.

“Two units, or 40 men, have arrived in Kos. Other reinforcements are being sent from other eastern Aegean islands,” a police spokesman said.

Earlier this week, police beat back migrants with truncheons and sprayed them with fire extinguishers to prevent a stampede as mostly Afghan and Syrian asylum seekers were being relocated to a local football stadium after camping along roads and beaches for weeks.

Mayor Kiritsis said the situation had “calmed” but was still tense as thousands of migrants await registration.

Greece is broke but now has to deal with a flood of migrants fleeing war and poverty.

“Since the beginning of the week extra immigration officials have been sent to Kos to speed up the administrative procedure,” said Mr Kiritsis.

“We hope that by the end of the week, the majority of the migrants can be registered and can leave the island.”

The island’s stadium and local gymnasium are being used to register the migrants, as well as the local police station.

Mr Kiritsis said the immigration officials were scheduled to leave the island by the end of the week.

Medical charity Doctors Without Borders (MSF) said its teams in Kos had seen “harassment of migrants and refugees in public spaces, including private security men forbidding them from sitting on park benches in the city centre”.

“MSF is very worried about how the situation is evolving in Kos,” MSF director of operations Brice de le Vingne said.

“What was previously a situation of state inaction is now one of state abuse, with police using increasing heavy-handed force against these vulnerable people.”

The UN refugee agency’s division for Europe said last week that 124,000 refugees and migrants had landed in Greece since the beginning of the year.

The agency said that Athens’ response to the problem had so far been “totally shameful”, with many of those landing on the eastern Aegean islands near Turkey forced to sleep in the open, without access to washing facilities and toilets.

Greek prime minister Alexis Tsipras last week said the refugee crisis surpassed the crisis-hit nation’s resources and called for European Union assistance.