The expansion also gives players the chance to take on a new type of character known as a Death Knight.
On the stroke of midnight, players - many of whom had queued for hours - got to pick up a copy of the game signed by the developers.
Scott Hamshere, from Bromley, should have been the first person in the UK with a copy of the game. He had started queuing at 6am and was the first in line. However, as the barriers were lifted, it was all too much, and he collapsed from exhaustion.
Instead it was 23-year-old Ben West, from Greenwich, who became the first person to own the game. Speaking to the BBC he said that it all came as a real shock.
"Up until that point it was a bit of an anti-climax in some respects. I expected to be second in line, and when I was first it was a real surprise," he said.
"I really feel for Scott, he was a real trooper, but in the end I think it just overwhelmed him. But we got chatting in the queue, he rang me afterwards, and we're going to meet up for a drink at some point."
Trailer for Wrath of the Lich King
For the vast majority of people, the night was an entertaining one, with many players saying they were going to play Warcraft all night once they got back home.
Developed by Blizzard Entertainment and launched in 2004, World of Warcraft has grown into one of the most popular of all online games, with more than 11m registered players.
"We've been looking forward to this launch event all year," said Blizzard's chief executive Mike Morhaime.
"This is one of the few opportunities we get to meet with players in person."
NEW CONTENT IN LICH KING
New continent of Northrend
Level cap increased to 80
New high-level Death Knight character class
Introduction of "Inscription" profession
New enemy: The undead armies of the Lich King
Introduction of siege weapons
New player-vs-player battlefields
The main focus of the expansion is the Lich King himself, Arthas Menethil, who many will recognise from Blizzard's real-time PC strategy games set in the Warcraft world.
Much of the content in the add-on game involves battling against the army of undead that Arthas controls.
Alongside the new content, Blizzard is also expected to start updating the graphics engine for WoW, making its cartoon-like imagery more realistic.
The new expansion pack will cost £24.99. However, it also requires a copy of the original game, the Burning Crusade expansion and a monthly subscription of £8.99.
In order to experience much of the expansion content including the Death Knight class, users need to be at a minimum of level 55 - meaning that novice and low-level players may have some work to do.
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