A few moments after Ben Mee put the Premier League team 1-0 up, dozens of German fans began storming through the segregation fence and hurling seats at the home fans.
Hannover fans, many of whom were wearing boxing-style gumshields and masks, fought with police and attempted to attack the English supporters.
There were also reports that some of the German hooligans were armed with knives.
Lancashire Police eventually advised the club to call off the game at their Turf Moor stadium and it was duly abandoned before the half time break.
"They called us in and said: 'Look, we're going to call it off for the safety of all involved, stewards, fans, police,' " said Burnley manager Sean Dyche.
"That was pretty early. The police were in the referee's room, called me, went through the procedure, and obviously we fully support the police's decision," he said.
The police are now appealing for mobile phone footage of disorder and say they are "determined to identify those responsible for causing injury and criminal damage."
"The disorder we saw has no place in football, and certainly not in Lancashire. Children and families were in attendance at what was a pre-season friendly match, which should have passed peacefully and without incident but which ended up being abandoned due to the behavior of some of the traveling Hannover fans. Both the constabulary and Burnley FC condemn this behavior," said Chief Superintendent Chris Bithell.
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One police officer suffered a head injury and was treated in hospital and two stewards were also injured, one of whom had a dislocated shoulder.
The Bundesliga club put out a statement on Sunday (August 7) in which they distanced themselves sharply from the violence.
"At the end of the first half of the season there was a clash in one stand of the stadium. On the orders of the local police, it was decided not to continue the game into the second half," they said.
"A total of 300 Hanoverians had traveled to Burnley. The police could no longer ensure security for the spectators in the stadium because 45 people among Hannover 96 fans were 'out of control,' " said Hannover's statement.
"We disassociate ourselves most strongly from the behavior of this group of people, who have immeasurably inflicted damage on the reputation of the club and also the team," said the statement.
The match was planned as a routine rehearsal for both teams before the first Premier League fixtures this coming weekend.
Burnley's first game is at Premier League champions Chelsea on Saturday (August 12) while Hannover's first game in the Bundesliga is the following weekend at Mainz. They play Bonner SC in the German Cup on Saturday.
"Together with the British authorities, Hannover 96 will use all legal possibilities to identify and prosecute potential violators," said Hannover's statement.
Lancashire Police has admitted it had got some intelligence before the game that some of the 300 Hannover fans were planning trouble at the game.
"We are now continuing to work closely with staff and managers at Burnley FC, and their co-operation has been very much appreciated. Similarly, we would like to thank the fans who co-operated and left the ground without incident once the game had been called off," said Chief Superintendent Bithell.
After the game was abandoned extra police were drafted in from as far away as Manchester to escort the German fans out of the stadium and out of the town.
Hannover 96 has little history of football violence, although their local derbies with Eintracht Braunschweig are known to be lively, and the incident was a mystery to seasoned Bundesliga watchers.