Some train connections between central Tokyo and airports servicing the Japanese capital were suspended Friday due to a broken rail on the Toei Asakusa Line, the operator said.

About 187,000 people were affected by the train service disruption on the Asakusa Line as 140 of its train runs were halted, according to the Tokyo metropolitan government, which operates the line.

[Corbis/Getty/Kyodo]

Trains were suspended on the same line last month after a similar issue was discovered.

Railway journalist Jun Umehara said that since broken rails tend to occur during summer and winter when severe temperature changes are observed, proper measures should be taken in the run up to the Summer Olympics and Paralympics next year in Japan.

"As the Asakusa Line is a critical train line connected to both Narita and Haneda airports, it could affect events at the 2020 Tokyo Olympics and Paralympics if similar things happen during the Games," he said.

Umehara suggested that replacement of rails with more durable ones at some vulnerable spots should be considered.

The broken rail was found between Sengakuji and Mita stations around 6:55 a.m. Friday, with services on the subway line fully resuming shortly before 10 a.m. following repair work, according to the metropolitan government.

Due to the disruption of services, Kyorin University's Faculty of Medicine pushed back the start of its entrance exam held at Tokyo venues, including in Minato Ward, by one hour.

The Asakusa Line runs between the northeast and southwest of Tokyo and shares its tracks with Keikyu Corp. and Keisei Electric Railway Co., which run trains to and from Haneda and Narita airports. Trains traveling between downtown Tokyo and the airports did not immediately return to the shared tracks.

The earlier suspension of Asakusa Line trains, on Jan. 20, was due to a broken track in the area near the popular Asakusa tourist district and the Tokyo Sky Tree tower.