SYDNEY (AP) — Australian police fired tear gas and shock grenades to quell asylum seekers who set fires at a detention center in a protest that the prime minister said Wednesday could hurt their chances of getting visas.

One man was arrested after Tuesday night’s riot by some 50 inmates at the Christmas Island detention center, an Australian Federal Police spokesman said.

He said the protesters “breached a number of compounds” within the center. They used improvised weapons and lit several fires, he said without elaborating.

Police retaliated with “bean bag” rounds, or lead pellets encased in cushions, tear gas and sound grenades, said the spokesman, who spoke on customary condition of anonymity. There were no injuries.

Protests frequently erupt at the overcrowded Christmas Island center, where Australia processes asylum seekers who have often fled poverty and war in the Middle East or Asia.

Tuesday’s protest — the fourth this year — is a reflection of the challenges faced by Australia’s policy of mandatory detention of refugees. Most of them risk their lives by undertaking perilous boat journeys from Malaysia or Indonesia, which they also enter illegally.

The U.N. Refugee Agency has urged Australia to seek alternatives to detention, saying automatic detention violates international law and does not appear to deter asylum seekers.

A Department of Immigration spokesman refused to say what sparked the latest protest or identify the nationalities of the protesters.

“Their reasons are their own. We are not going to speak for them,” said the spokesman, also speaking on the same condition of anonymity.

He said all detainees involved in the protest returned to their compound and the external perimeter of the compound was not breached.

Prime Minister Julia Gillard condemned the riot, saying the asylum seekers cannot speed up their visa application process “by misbehaving.”

“If you commit criminal offense it will be counted against you,” she told reporters, referring to a new “character test” that bars prospective immigrants from the country if they have a criminal record.

“Indeed, it will prevent them from getting a visa,” she said.

In March, more than 200 detainees demanding visas set fire to buildings and tried to escape from the center, which is located in the Indian Ocean and houses some 1,100 inmates. It is located closer to Indonesia than the Australian mainland, which is 1,600 miles (2,600 kilometers) away.

Another protest broke out last month and one more occurred Sunday, when 11 inmates climbed onto the roof at the detention center’s main compound, which mainly holds single adult males.