Sheffield Wednesday upset Newcastle to reach the FA Cup fourth roundThe government's advisor on safety at sports grounds is "concerned" by reports of overcrowding at Hillsborough during the FA Cup tie between Sheffield Wednesday and Newcastle.
Newcastle fans claimed on social media there was a lack of stewarding in the Leppings Lane End before Saturday's kick-off and that they were crammed in.
The Sports Grounds Safety Authority (SGSA) said it will begin a review.
The Football Association is also looking into the reports.
Ninety-seven Liverpool fans died after a crush in the stand in April 1989, during the FA Cup semi-final between Liverpool and Nottingham Forest.
"We are concerned by reports of overcrowding and crushing at the FA Cup tie between Sheffield Wednesday and Newcastle United at Hillsborough Stadium on Saturday," said an SGSA spokesperson.
"The SGSA is now working with the club, Sheffield City Council and the Safety Advisory Group to review the event, learn any lessons and ensure a safe environment for football fans."
The FA will speak to officials from Sheffield Wednesday and Newcastle, the police and safety authorities about the incident.
There were 4,500 Newcastle fans in the Leppings Lane End for the game, which ended in a 2-1 win for the League One hosts against their Premier League opponents.
The Newcastle United Supporters' Trust has asked anyone involved to contact them with details of their experience.
