The Clarets suffered their joint heaviest defeat of the campaign as they continue to find it tough going in the Professional Development League.
Boss Michael Duff had three teenage trialists in his side as he continues to try and bring players on at development level.
But in a first season of competitive football for the under-23s it’s proving a testing learning curve as the Blues handed out a sixth defeat in seven games.
Birmingham have hit a bit form to pull away from the bottom end of the league’s northern division and are now unbeaten in five games.
But they won’t have had it much more comfortable than they did at a freezing cold Barnfield training centre as they strolled into a 3-0 half-time lead and added two more without reply after the break.
The visitors’ opening goal needed a touch of luck as an attempted cross from Remeao Hutton caught the wind and flew past Connor Mitchell, who was unable to keep the ball out at his near post.
Mitchell then saved from Wes McDonald with Jack Storer steering the rebound wide, before one of the Clarets’ few clear-cut chances saw Ntumba Massanka make space for a shot which was deflected wide.
And Birmingham, whose side boasted a couple of players with first-team experience as their best youngsters were held back for a last-16 FA Youth Cup tie on Friday night, then took complete control with two goals in five minutes just before the break.
Kyle McFarlane had already cracked a shot against a post when former Fulham youngster McDonald made it 2-0 with a vicious long-range strike into the roof of the net.
And then in stoppage time it became 3-0 when McDonald set up the lively McFarlane for a measured finish.
The Clarets sent on Ali Koiki at the break to try and inject some life into their performance but with an hour gone it was 4-0.
Charlie Lakin whipped in a free-kick which was deflected past Mitchell.
But the impressive Blues’ midfielder will be claiming the goal and certainly got the last one as Birmingham went 5-0 up with 15 minutes to go.
This time he was given time and space to line up a shot which he directed into the bottom corner.
But for a smart save from Mitchell to keep out another McDonald effort it could have been six – equalling the number Sheffield United put past the Clarets in October.
At the other end a header from Massanka which went over the top from a Koiki cross was all Burnley could muster in response.
Dwight McNeil, fresh from his recent inclusion in the senior squad, showed a willingness to get on the ball whenever possible and Massanka did his best to work the visitors' defence.
But with few other plus points, the Clarets suffered a 10th defeat of the campaign to stay bottom of the table – only their recent Premier League Cup win at Swansea and possible progress in that competition offering solace in a difficult run of results.
Burnley: Mitchell, Birch, Trialist, Younger, Trialist, Jackson (Koiki ht), N’Guessan (Nabi 75), McNeil, Bayode, Trialist (Wood 75), Massanka. Substitutes: King, Clarke.
Birmingham City: Weaver, Dacres-Cogley, Martin, Maxwell, Seddon, Lakin, Hutton, Bernard, McFarlane (Lubala 60), Storer (McCoy 73), McDonald. Substitutes: Landers.
Referee: Leigh Doughty