West Ham players before their Europa Conference League semis.[Twitter, West Ham]

EUROPA CONFERENCE LEAGUE

Substitute Pablo Fornals scored deep into stoppage time for West Ham to beat AZ in Alkmaar 1-0 in the second leg of the Europa Conference League semifinals and send the Premier League club to a European final for the first time in 47 years.

The aftermath was then marred by crowd trouble when some Dutch supporters tried to storm into the area reserved for friends and family of the visiting players behind the dugout after the final whistle.

West Ham players including Michail Antonio, Said Benrahma, Aaron Cresswell and Flynn Downes climbed over the advertising boards in a bid to stop the trouble.

"I can't explain what happened and why it happened," West Ham manager David Moyes said. "I can only say the players were involved because it was the family section and most of their family and friends were in there. That was probably the reason for the reaction."

West Ham will face Fiorentina in the final in Prague on June 7.

The Hammers have been waiting for a European trophy since the 1965 title in the European Cup Winners' Cup and reached the final in the same competition again in 1976.

Fiorentina also needed extra time to advance, with substitute midfielder Antonin Barak netting the decisive goal in the 129th minute to secure a 3-1 win at Basel. Fiorentina trailed 2-1 from the first leg but reached its first European final since 1990.

Fiorentina's Nicolas Gonzalez was unmarked at the far post to put the visitors 1-0 ahead after a corner kick from Cristiano Biraghi in the 35th.

Forward Zeki Amdouni leveled the score at 1-1 for Basel 10 minutes into the second half, a result that would have sent the Swiss club to a European final for the first time. The Swiss forward scored in six of the last seven games in the knockout stage, including the first leg of the semifinals.

Gonzalez scored his second goal at St.Jakob-Park with a low left-foot shot in the 72nd to force extra time.

Fiorentina's win means Italy has a team in the final of all three UEFA competitions, with Inter Milan facing Manchester City in the Champions League title match.