Nineteen-year-old Erling Haaland followed up his debut hat trick for Borussia Dortmund by scoring two more, again as a substitute, in a 5-1 demolition of Cologne in the Bundesliga on Friday.

Jadon Sancho, another 19-year-old, was also on target with his 11th Bundesliga goal of the season -- his eighth in his last eight outings -- and added another assist as Dortmund outclassed the hapless Billy Goats.

Raphael Guerreiro and Marco Reus set Dortmund on the way with first-half goals as they cut the gap between themselves and leaders RB Leipzig to four points ahead of Leipzig's visit to Eintracht Frankfurt on Saturday.

Haaland, the first player ever to score five goals in his first two Bundesliga appearances, has come on in the second half both times and spent a total of 59 minutes on the pitch.

He scored 28 goals in 22 games for Austrian side FC Salzburg in the first half of the season before joining Dortmund in January.

Both first-half goals came from long passes upfield from defender Mats Hummels, who also saw a header hit the bar.

Following the match, Reus told Dazn: "I think it was a step ahead in footballing terms. We scored many goals again.

"Haaland's very calm, relaxed. Works very hard. Also on his fitness. He did not train that much in December. It's wonderful for him. Two games, five goals."

Guerreiro opened the scoring in the first minute from a Sancho assist and Reus doubled their lead before the half hour, the referee awarding the goal after a VAR review after initially disallowing it for offside.

Sancho increased the lead three minutes after the re-start and Mark Uth pulled one back with a superb volley from a tight angle, before Haaland scored a poacher's goal, turning in a rebound for in the 77th minute.

The Norwegian then latched onto a through ball, raced past goalkeeper Timo Horn and turned the ball in from a narrow angle.

Dortmund keeper Roman Burki joked about his new teammate: "It's a shame his figures are already dropping. Three goals, two goals. I just don't hope it's only one next week."

Both first-half goals came from long passes upfield from defender Mats Hummels, who also saw a header hit the bar.