Two students are in Dunedin Hospital after falling off a roof and a balcony of separate flats during celebrations in the city.
A St John spokesperson said an ambulance and rapid response vehicle went to a Park Street address about 4.15pm.
The patient was taken to Dunedin Hospital in a serious condition.
Dunedin police sergeant Aaron Burgess told Checkpoint the intoxicated student fell off a balcony of Park Street flat and was injured severely.
He said they fell backwards off a second storey balcony and landed on their back.
They were unconscious for some time, he said.
Burgess said there has been rain today, making roofs slippery.
"We've got in excess of 2000 or 3000 students wandering around the streets ... all dressed in green or wandering around with alcohol or intoxicated, rubbish is everywhere.
"Some of them are in party locations, and some of those parties are probably in excess of 100 people, which we're trying to control as well as we can, but we're obviously limited with our staffing numbers at the moment too.
"Omicron is really affecting our resources as well and we can't be everywhere at all times."
He said there was a "blase attitude" among students about Covid-19 restrictions.
"There's not a mask in sight ... no social distancing. There's sharing of vapes and bottles, and unfortunately, it's not something we can completely control."
Shortly after 2pm a 19-year-old man suffered serious back injuries after falling from the balcony of a Castle Street flat.
St John Otago Southland area operations manager Doug Third said student parties were adding to ambulance staff's workload at a time when they were already stretched.
"St John has responded to several 111 calls regarding incidents associated with St Patrick's Day student parties in Dunedin today," he said.
"This has put added pressure on the emergency ambulance service at a time when we are already experiencing unprecedented demand due to the Omicron outbreak. As a result, St John has rostered additional emergency vehicles in Dunedin today to ensure our ambulance officers can continue to respond to all life-threatening calls.
"St John encourages everyone attending St Patrick's Day events to drink responsibly, look after each other and ensure they have a safe way to get home."
Police officers are also being kept busy dealing with the large numbers of intoxicated young people in the city's student quarter.
Sergeant Anthony Bond said police and Fire and Emergency were called to another flat in Castle Street earlier in the day to deal with a couch fire.
"At 2.45pm police attended another Castle Street gathering and assisted ambulance staff as a 19-year-old male fell off the roof and is in hospital with back injuries. This is a reminder that climbing on roofs at any time is risky behaviour and even more so when intoxicated," Bond said.
"Overall the behaviour has been good, but unfortunately there have been a few idiots that police have had to speak to to remind them of acceptable behaviour, and so far no arrests.
"Extra police are rostered on today and will be having a presence in and around the North Dunedin area, as well as breath testing motorists in and around Dunedin to ensure those that do choose to drink, don't drive."
Police are also investigating a couch fire on Castle Street that started around 9am.
Bond said many young people in the area had been drinking since early this morning and there was a large gathering at the address where the fire was lit.
"There are large amounts of people wandering around the streets, intoxication is getting up there and unfortunately there was one fire in the front of a residential property in Castle Street around 9am, which was of concern to us and [Fire and Emergency].
"So we're still monitoring the situation and doing foot patrols in and around the North Dunedin area."
Bond said in the past few years police had taken "a very hardline approach" to fires being lit in the university area.
"Unfortunately, there was a large gathering at the address at the time, so information is limited but the investigation is ongoing."
There were also a number of large gatherings in the area, including at Brackens Lookout - which regularly attracted St Patrick's Day party-goers.
"It is the same as previous years, where a large number of people are drunk by 9am which is disappointing and they're putting themselves in danger as well being so close to the one-way systems," Bond said.
"It seems very similar to previous years. There are a number of students that have caught Covid and have been through their isolation period and are out the other side looking for some good times and unfortunately due to the red [light] settings those large events aren't happening at the moment to entertain them.
"So days like today are when they're taking the opportunity to party but they are still gathering in excess of the 100-person limit."
Covid-19 remained a concern in the area with numerous flats still isolating, he said.