Trains on Metra's BNSF Line were unable to enter or exit Chicago's Union Station during the afternoon rush hour Tuesday, less than an hour after trains on the line were halted near suburban Cicero after a pedestrian was struck.

Just before 6 p.m., Metra said most trains were moving, but big delays were expected.

Metra did not say why trains were unable to depart or arrive at the station Tuesday.

"BNSF Railway customers are advised to stay at the office or another location until this problem is corrected to prevent overcrowding," Metra said in an alert. "If possible, Metra customers may wish to seek alternate forms of transportation."

All trains on the BNSF Line were also halted earlier Tuesday afternoon after a pedestrian was struck by a train near suburban Cicero.

Outbound train No. 1239, which was scheduled to arrive in Aurora at 4:16 p.m., but was stopped near Cicero after striking a pedestrian, Metra said in an alert on its site.

All inbound and outbound trains were stopped after the incident, and extensive delays were expected, the transit agency said.

Metra also implemented its overcrowding prevention plan at Union Station. All BNSF passengers were asked to go to the loading/staging area prior to boarding. Southwest Service and Heritage Corridor passengers were allowed to enter the South Concourse.

Metra did not have exact numbers for how many riders would be affected by the delays, but said that the BNSF line provides 54,600 rides each day. Metra spokesperson Meg Riley estimated that Tuesday's delay could impact as many as 26,000 people.