LESBOS, Greece — Greek riot police fired tear gas Thursday at angry protesters on the island of Lesbos who tried to topple a police bus during a demonstration against a European Union migration policy.

The protesters were among 2,500 demonstrators who gathered in Lesbos’ main port as Prime Minister Alexis Tsipras arrived to speak at a conference.

A large contingent of riot police formed a cordon to block the protesters from advancing farther, and scores of them then tried to push over a police bus in clashes that lasted more than an hour.

No arrests or injuries were reported.

Officers fired tear gas and earlier had discharged several flash grenades.

A general strike Thursday virtually shut down the island to protest a 2016 agreement between the EU and Turkey that has left thousands of asylum-seekers stranded on Lesbos.

Under the deal, migrants arriving on Greek islands from Turkey are held and face deportation to Turkey unless they successfully apply for asylum in Greece.

The deal has created a massive backlog, angering people on Lesbos and other Greek islands.

“It has gone too far. Every day buses (with refugees) arrive, and they’re full,” protester Yannis Vaxevanis said.

“The (government) has to do something and take the people somewhere else.”

Most businesses, shops, cafes and local government offices were shuttered in the main town of Mytilene. The only sign of normality was that police officers were still on duty, and the local tax office was open.

Stores were also closed in protest on the nearby island of Chios.

More than 15,000 migrants and refugees remain stuck on Lesbos, Chios and three other islands, most staying in severely overcrowded camps.

“Thousands of people are still living in appalling conditions with limited access to medical facilities,” the aid group Doctors Without Borders said.

Conditions at the largest refugee camp in Lesbos, the group said “were putting the health and lives of people stranded on the island at risk.”

Additional police officers, including anti-riot units, were sent to Lesbos and took up positions around Mytilene.

Supporters and opponents of the government used vans fitted with loudspeakers to promote the protest as well as a speech planned by the prime minister later Thursday.

The government has promised to move thousands of asylum-seekers to the mainland but says the effort will take several months to implement — requiring additional staff and more shelter sites.

The number of daily arrivals continues to rise on the island and Greece’s land border with Turkey.

Authorities said 53 people thought to be from Iraq and Syria were picked up Thursday after a yacht used to smuggle them into the country ran aground on a remote mainland beach in northeastern Greece.