Police in the Republic of Ireland said they were still adding up the number of public-order arrests from Tuesday's festivities but said the total would easily exceed 200, typical for recent years.
Police in Northern Ireland clashed with some of the British territory's most privileged youth - hundreds of students at Queen's University, the major college in Belfast - in what authorities called the worst public drinking-related confrontation of any recent St. Patrick's Day.
Nineteen teenagers and 20-somethings, mostly Queen's students, were arrested during several hours of clashes with riot police. Belfast police Superintendent Chris Noble said most were still sobering up Wednesday in their cells, while five were arraigned in court on charges of riotous behavior.
Noble said police expected to arrest more students in coming days after analyzing their surveillance TV footage.
"We will not abandon an area to drunken thugs," he said.
Officers of the Police Service of Northern Ireland donned full riot gear, including flame-retardant suits, to drive about 1,000 students back into their rented red-brick homes in a neighborhood called the Holy Land directly beside Queen's University.
The area - so named because it has streets named Jerusalem, Damascus and Cairo - has suffered St. Patrick's riots for several years running, but older residents and politicians agreed this year's was by far the worst.
Leaders from the British Protestant and Irish Catholic sides of Northern Ireland's power-sharing government demanded that Queen's expel students at the center of the trouble. Until now university authorities have issued warnings or fines to students only.
"I toured the area myself last night and was absolutely disgusted. The place was like a war zone. It was an atmosphere of intimidation and mayhem," said Protestant politician Reg Empey, minister for higher education in the power-sharing government.
The Irish Republic's police commander, Commissioner Fachtna Murphy, said it suffered one of its most dangerous holiday periods on the roads amid increased levels of drunken driving.
He said since Friday police had arrested 346 suspected drunk drivers and 72 for dangerous driving, while eight people died in crashes, compared to three in the same period last year.
The Dublin Fire Brigade said its officers were pelted with stones, cans and bottles in several public housing projects overnight as they dealt with 46 fires, mostly smashed-up cars that had been set ablaze.
Ambulance crews dealing with more than 200 emergency calls - including a dozen stabbings involving knives or broken bottles - said they also suffered physical and verbal abuse as they responded to booze-fueled bloodshed.
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