What exactly happened?
England defender Tyrone Mings appeared to glance over his shoulder and look towards a section of the crowd after making a pass and 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 boss 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 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.
