Limited express train services connecting Narita airport with major cities in the capital region were halted Thursday after unusual chunks of concrete were discovered in a tunnel on the JR Yokosuka Line, the railway operator said.

East Japan Railway temporarily suspended its services between Yokohama and Tokyo stations on the Yokosuka Line, as well as the Narita Express.

The concrete chunks, discovered in the capital's Minato Ward by railroad workers at around 3:10 a.m., are believed to be part of ventilation equipment, according to JR East.

Efforts to address the issue continued until Thursday afternoon.

==Kyodo

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