Son's treble was particularly fitting given the South Korean was subjected to abuse from Millwall supporters.

The visiting fans sang "DVD" and "You're selling three for a fiver" at the 24-year-old during the first half, thought to be referring to traders of bootleg copies of films.

Christian Eriksen, Kane's replacement, broke the deadlock before Son netted either side of half-time.

Dele Alli added a fourth and there was even time for Vincent Janssen to grab his first Tottenham goal from open play before Son hit his third late on.

Spurs will now await Monday's draw for the semi-finals where they can meet Manchester City, Arsenal or the winners of Chelsea and Manchester United, who play on Monday.

Much of the talk in the build-up surrounded security given the history of animosity between these two London clubs, and there was a heavy police presence around the ground before kick-off.

More than a dozen police vans lined the front of the stadium to contain supporters, who exchanged unpleasantries as well as throwing bangers and flares at each other.

On the pitch, however, any tension quickly disappeared as Tottenham ran riot to maintain their unbeaten record at home and win what is set to be their last ever FA Cup fixture at White Hart Lane.

Kane's injury though could wreak havoc with their ambitions in both this competition and the Premier League.

It was his right ankle that caused him to miss seven weeks earlier in the season, and he now risks missing next weekend's home game against Southampton and England's fixtures against Germany and Lithuania later this month.

Pochettino made four changes from the side that beat Everton as Michel Vorm, Kieran Trippier, Harry Winks and Son came in. Hugo Lloris, Kyle Walker, Mousa Dembele and Eriksen made way.

Tottenham flew out of the blocks as Winks and Kane both saw shots parried by Tom King before Son weaved his way through but was also denied from an acute angle.

The hosts' positive start was checked, however, when Kane was forced off in the sixth minute. The striker had fallen awkwardly over the sliding Jake Walker and, hunched off the pitch, appeared to be clutching his right ankle.

Kane shook his head at Pochettino and was swiftly replaced by Eriksen as Son pushed into the role of lone striker with Alli just behind.

Alli was unfortunate not to win a penalty, twisting away from Tony Craig and then tumbling to the ground after the defender had tugged his shirt, but it would not be long before Millwall's resistance was broken.

Steve Morison had just guided a shot wide after Dier failed to deal with a long punt downfield when, with half an hour gone, substitute Eriksen broke the deadlock.

Byron Webster's header was chested down by Alli but Eriksen quickly took charge, instinctively half-volleying into the bottom left-hand corner.

Victor Wanyama almost doubled Tottenham's lead when he headed Eriksen's corner against the crossbar and it was towards the end of the half that some of Millwall's chanting turned sour.

It was fitting then that Son responded by scoring two sumptuous goals.

The first started with the forward miscontrolling but he quickly recovered, darting inside Webster and unleashing a left-footed strike into the top corner.

His second after half-time was no less emphatic, albeit more straightforward, as Trippier chipped a 40-yard pass over the top and Son, drifting in behind, volleyed home first time for Tottenham's third.

Alli added a fourth, touching home Eriksen's cross from close range, before Janssen drew the biggest cheer of the afternoon when his swivel-shot crept inside King's near post.

Son then sealed his hat-trick in stoppage time when his volley sneaked through the hands of King. With Kane injured, Spurs will hope his form is a sign of things to come.