Dutch police have warned West Ham fans without tickets not to travel to the ground tomorrow night.
Police intelligence suggests as many as 5,000 West Ham fans are set to travel to Holland.
The club has an away allocation of just 975 at the 19,500-capacity AZ Stadion, five times fewer than the number expected to make the trip,
Local authorities are laying on buses to take West Ham fans from the city centre to the stadium and back to Alkmaar’s main train station post-match.
Many Hammers fans are expected to stay in the Dutch capital Amsterdam, 40km south of Alkmaar, before travelling in by train for the match.
West Ham go to AZ Alkmaar on Thursday night leading 2-1 from the first leg of their Europa Conference League semi-final as the Hammers look to reach their first European final in 47 years.
Players trained at Rush Green this morning before flying to Holland this afteernoon.