TOKYO — An express train entering a station in Japan hit and killed four people who were doing weed control work on a railway track Thursday, officials said.

The accident occurred at Shin-Kanuma Station, north of Tokyo, on the Tobu Nikko Line, and involved the Tokyo-bound Spacia express train, the Tochigi prefectural police said.

The four — three workers and a supervisor — were rushed to a hospital but later pronounced dead, according to police and train operator Tobu Railway Co.

Six other people at the site — two other workers, three on lookout duty and an on-site supervisor — were safe, Tobu Railway said. The group had been assigned to spray herbicide. About 50 passengers on the train were also uninjured.

Railway officials said it was unclear why the workers did not leave the site when the train was approaching, or what the lookout people were doing. They said they are cooperating with authorities investigating the cause of the accident.

Those on lookout duty are supposed to warn fellow workers of an approaching train and let them evacuate. They wave a flag to the train, then its driver sounds the horn to signal awareness and moves on with caution. Initial accounts from the workers suggested possible miscommunication, but what exactly happened Thursday before and during the accident was still under investigation, Tobu officials said.

Fatal train accidents are rare in Japan, which has a reputation for safe and punctual transportation.

Takao Suzuki, head of Tobu’s railway business division, apologized for the fatal accident. “We take this severe accident seriously and we will ensure preventive measures and never let this happen,” he said.

Trains on the line were suspended for several hours, but services resumed later Thursday, officials said.