The blue touch paper was lit just 90 seconds into the game when Hemp headed home Chloe Kelly’s cross from the right, before White doubled the lead with a typically clinical first-time finish two minutes later.
Substitute Sam Mewis added further gloss to the scoreline by heading home a third in the 89th minute, handing Gareth Taylor's side a healthy advantage going into next Thursday's second leg in Florence.
While City were delving into the unknown by taking on a side they had never faced in a competitive fixture, it didn’t take long for some of the usual suspects to put us in the driving seat.
Chloe Kelly raced past Greta Adami to the byline before floating a cross into the far post inside two minutes, which was met by the familiar late run of Hemp.
The winger powerfully headed the inviting ball back across goal and into the net to give Gareth Taylor’s side the dream start at the Academy Stadium.
Just two minutes later it got even better when Hemp turned from scorer to provider, whipping a vicious cutback into the near post from the left, which was duly smashed into the roof of the net by the onrushing White.
Not content with one, White could have even completed a hat-trick inside ten minutes, forcing a smart save from Katja Schroffenegger after being teed up by Kelly before flashing a glancing header just over the bar moments later.
After that devastating first ten minutes, the visitors began to slowly find their feet, but they continued to be pegged back inside their own half against a relentless City side.
And Schroffenegger once again had to be at her best after 20 minutes, blocking Hemp’s goal-bound effort after the winger had met Georgia Stanway’s fizzing ball across the box on the volley.
While the half failed to yield another goal, Gareth Taylor’s side continued to zip the ball around in pursuit of a further opening, with Fiorentina applying a more intense press in response.
That new found defiance from Antonio Cincotta’s side was typified by a full blooded clash between Steph Houghton and La Viola forward Sara Baldi towards the end of the half, with both players landing awkwardly after an aerial duel.
Thankfully our skipper was able to dust herself down and continue, but unfortunately the Italian forward was forced off through injury with first half stoppage time approaching.
But despite that setback, the visitors almost halved the deficit five minutes after the restart when Frederikke Thogersen raced through on the right following a swift counter.
Thankfully, from a City perspective, the Danish international was unable to cap off Fiorentina’s bright start with a goal, failing to hit the target under pressure from the rapidly retreating Abby Dahlkemper and Hemp.
Gareth Taylor’s side remained in control, and could have added a third when Houghton was presented with a free-kick in a dangerous area.
The skipper’s effort had Schroffenegger scrambling, but landed a couple of inches wide of her near post as the game ticked over the 70-minute mark.
City continued to huff and puff for further daylight between the two sides and they were rewarded in the game's dying embers.
Substitute Mewis was back among the goals with stoppage time approaching, nodding home from Kelly's cutback to put us in the driving seat to reach the Champions League quarter finals.
How we lined up
CITY XI | Roebuck, Bronze, Houghton (c), Dahlkemper (Morgan 63’), Greenwood, Coombs, Stanway, Weir (Mewis 64’), Kelly, Hemp (Lavelle 64’), White
SUBS | Taieb, Keating, Walsh, Mannion, Beckie, Davies
FIORENTINA XI | Schroffenegger, Cordia, Quinn, Adami (c), Thogersen, Vigilucci, Neto, Middag, Zanoli (Monnecchi 77’) , Sabatino, Baldi (Clelland 45’)
SUBS | Ohrstrom, Tortelli, Breitner, Piedmont, Forcinella, Pastifieri, Papi, Mani
Player of the match: Chloe Kelly
Capable of taking her marker on or whipping a delicious ball into a dangerous area in equal measure, our right winger was once again at the centre of all things good for City.
Linking up in devastating fashion once again with her fellow winger Hemp for the opener, Kelly notched up her ninth and tenth assists in an impressive debut season at the Academy Stadium.
Lauren Hemp's fine form continued against La Viola, the winger has now scored 8 goals in her last 9 matches in all competitions.
City have let in just five goals all season at the Academy Stadum, and have not conceded on home soil since mid-December.
The first leg victory over Fiorentina was our sixth in a row, meaning Gareth Taylor’s side are now currently on their longest winning run of the season so far.
The games are coming thick and fast for Gareth Taylor’s side, with a Women’s Super League home clash against Everton next up on Sunday.
The second leg of our Champions League tie with Fiorentina will then take place on the following Thursday in Florence.
News about Man City v Fiorentina
White: City’s attacking prowess a striker's dream!
Ellen White says it is a ‘privilege’ to spearhead City’s superb attacking trio. Read more.
City 3-0 Fiorentina: Full-match replay
Watch the full 90 minutes of City's Champions League last 16 first leg victory over Fiorentina on CITY+. Watch more.
City 3-0 Fiorentina: Match highlights
The best of the action from our convincing Champions League last 16 first leg victory over La Viola... Watch more.
Taylor: The sky is the limit for 'street fighter' Kelly
City manager Gareth Taylor insists Chloe Kelly is capable of reaching the very highest level after another standout performance in our 3-0 Champions League last 16 first leg win over Fiorentina. Read more.