Andy Carroll and substitute Peter Lovenkrands struck two goals each and Gabor Gyepes put through his own goal, before shell-shocked Cardiff managed a late Aaron Wildig consolation.
Within 15 minutes any thoughts of a Cardiff win were dead and buried as table-topping United surged into 3-0 lead.
Newcastle raced ahead after just two minutes when Danny Guthrie's back-post corner was returned by Fitz Hall for a Kevin Nolan to head goalwards, where Carroll finished off.
Three minutes later and Wayne Routledge found Carroll on the edge of the area and he cannoned a drive against the upright and central defender Gyepes could only watch in horror as the ball smashed against him and went into the net.
The big Cardiff following were stunned and it got worse when they saw their side torn to shreds as Carroll struck again after 15 minutes.
Danny Simpson surged down the right to whip in a delightful cross that saw Carroll rise high to powerfully head in his second.
United seem to have a thing about racking up 3-0 home leads against Welsh sides inside the first quarter hour, having done the same against Swansea in November.
Cardiff only managed one first-half effort on target, though they did hit the woodwork twice with a screaming Ross McCormack volley and a speculative Adam Matthews cross that Steve Harper misjudged which struck a post.
Skipper Michael Chopra flashed an early second-half warning with a shot that was deflected goalwards off Hall and turned over by Harper.
The disappointing Leon Best made way for Lovenkrands on the hour mark and, while Best never looked scoring, the Denmark international took a mere eight minutes to make it 4-0, racing on to a through ball and flicking it beyond David Marshall.
And it got even better for Lovenkrands seconds after Carroll was denied a hat-trick following a goal-line clearance by Gyepes.
The Dane picked up the ball on the right after 81 minutes and cut inside to curl a delightful shot beyond Marshall, that struck the far post and went into the net to make it six goals in his last four games.
Cardiff did finally grab a consolation deep into the game when substitute Wildig finished well, but it was far too little too late.