The Euro 2020 qualifier between Bulgaria and England was temporarily halted by the match referee in the first half on Monday under a three-step UEFA protocol to tackle racist abuse from the crowd.
Britain's Sky Sports television said racist chanting was heard from the stands and reported by England players to manager Gareth Southgate, with the referee informed and a public announcement made.
The second step of the protocol, with the match temporarily suspended, was carried out after a further complaint was made by Southgate.
Sky Sports reporter Rob Dorsett said he had heard monkey chants on six occasions when England players Tyrone Mings, on his debut, and Marcus Rashford were in possession of the ball.
"I heard one fan clearly shout "Hey, monkey" as Mings passed the ball," he said.
The UEFA protocol involves the referee first halting play and making an announcement to the supporters to immediately stop racist behaviour.
The second step sees the match suspended for some time and both teams sent to the dressing room if the abuse continues, with another warning given to the fans.
In the third and final step, the referee decides to abandon the match.
England were leading Bulgaria 4-0 at halftime in the Group A match.
Bulgarian captain Ivelin Popov was seen talking to fans through the metal fence at the break. A number of people were seen leaving the stands.
"You can talk about protocols, but I'm sitting here feeling sick to my stomach. It's heart-breaking," said former Manchester United and Ireland midfielder Roy Keane, a pundit for ITV television.
"The game is done now but I feel physically sick watching that."
Former England striker Ian Wright, also a pundit for the broadcaster, said it was "a terrible day for the Bulgarian people but a great one for trying to tackle racism.
"We can see those bans mean nothing, we are seeing a set of fans that do not care and need educating. That's what has got to happen," he added.
