England's Euro 2020 qualifier in Bulgaria was halted twice as fans were warned about racist behaviour including Nazi salutes and monkey chanting.
The first pause came in the 28th minute with England leading 2-0.
A stadium announcement then condemned the abuse before stating the match would be abandoned if it continued.
However, the game was stopped again in the 43rd minute before restarting after discussions between the referee and England manager Gareth Southgate.
England went on to win 6-0 in Sofia to strengthen their place at the top of Group A.
'One of the most appalling nights I've seen in football'
Football Association chairman Greg Clarke was at the game and witnessed the abuse first hand, saying it had left a number of the England players and staff visibly upset.
"I heard examples of appalling racist chanting," he said.
"I was looking at a group of people, all in black – about 50 of them – who were making what looked like political fascist gestures. I couldn't be sure, it was 100 metres away but it looked appalling.
"I've spoken to one or two of the players and I've also spoken to one or two of the backroom staff, because we don't just have a multiracial team, we have a multiracial backroom staff.
"They were visibly emotionally upset, and I spoke to Gareth after the game too and I offered him our full support."
Clarke says he expects European football's governing body Uefa to conduct a thorough review of the incident.
"Uefa, who I've spoken to throughout the game, at half-time and at the end of the game, will be carrying out a thorough investigation to make sure this appalling scene of terrible racism is treated appropriately," he said.
In a statement, the FA confirmed England players were subjected to "abhorrent racist chanting" and that it was "unacceptable at any level of the game".
England defender Tyrone Mings, who was making his international debut, said the players had decided as a group at half-time to continue the game.
"Just before the end of the first half the appropriate next step was to return to the changing room," he told BBC Radio 5 Live.
"We made a common-sense decision to play the remaining few minutes and decided at half-time. Everybody made the decision. The manager, the team, the supporting staff. We spoke about it at half-time and we dealt with it and escalated it in the right way.
"I am proud of how we dealt with it and took the appropriate steps."
The Vasil Levski Stadium was subject to a partial closure for this match after Bulgaria were sanctioned for racist chanting during qualifiers against Kosovo and the Czech Republic.
The build-up to the game had been dominated by concerns of potential incidents of racism, with England striker Tammy Abraham saying the players would be prepared to walk off the pitch if they were targeted by racist abuse.
Southgate held a meeting with his players over the weekend to underline the Uefa three-step protocol in dealing with racist incidents – but the subject provoked an angry response from the Bulgarian football authorities.
Bulgaria coach Krasimir Balakov had accused England of having a bigger racism problem than his own country.
What exactly happened?
After making a pass, England defender Mings glanced over his shoulder and could be heard calling towards the touchline: "Did you hear that?"
Within minutes the game was stopped.
Striker Harry Kane was in conversation with referee Ivan Bebek on the halfway line while a stadium announcement was made to condemn racist abuse and warn fans that the game could be abandoned if it continued. At the same time, England manager Southgate was talking to a number of his players.
The game resumed but was stopped again just before half-time. Southgate and several England players were in discussion with match officials before the game was restarted for a second time.
A group of Bulgaria supporters wearing black hooded tops – some wearing bandanas covering their faces – started to leave the stadium after the game was halted for a second time. BBC Radio 5 Live reported that some made right-wing and racist gestures while heading towards the exits.
After six minutes of time added at the end of the first half because of the delay, Bulgaria captain Ivelin Popov was seen in a heated debate with a section of home supporters near the tunnel while the rest of the players headed for the dressing rooms for half-time.
What is Uefa's protocol for dealing with incidents of racism?
Uefa has a three-step protocol, introduced in 2009, in place for dealing with such incidents in matches.
For the first step, the referee will speak to the stadium announcer and demand the halting of racist behaviour.
If it continues, the referee can take the players off the field into the dressing rooms for a period of time and the stadium announcer will make another address.
If it still continues, the match will be abandoned.
In this incident, the first step was taken while the players were asked if they wanted to come off the pitch, but decided to continue.
Southgate said: "I explained to the players that if anything else did happen in the second half we would be Read More – Source