An express train derailed in northern Japan on Sunday, killing two women and injuring more than two dozen other people, officials said. Strong winter winds were reportedly suspected as a cause.

Several more people were still believed trapped in the wreckage, their conditions unknown.

The injuries of the survivors outside the wreckage did not appear to be life-threatening, but it was not known whether those trapped inside were still alive, Yamagata police spokesman Yoshikatsu Oe said.

Five cars of the six-car express train derailed at 7:20 p.m., three of the cars toppling onto their sides in Yamagata prefecture, about 180 miles north of Tokyo, officials said. The train was en route from northern Akita prefecture to Niigata prefecture.

Most of the injured passengers were on the first two cars, Oe said. It was unclear how many passengers were on the train; one official said it was 30, but the tally of the injured and trapped indicated it was more.

Transport Ministry official Hiromi Mishima said the cause of the accident was not immediately known, and officials were still trying to assess the extent of the damage.

However, Yamagata police official Yasuhiro Sugiu said there had been high-speed wind warnings for the area. NHK quoted a train conductor as saying a strong gust of wind hit the train just before the accident.

Japan in recent days has suffered from unusually heavy snowfall, and blizzards have led to the deaths of eight people. But snow did not appear to be a factor in Sunday's crash. NHK footage of the wreckage site showed the train derailed in a rural area with only patches of snow on the ground.

A train derailment April 25 in Amagasaki, western Japan, killed 107 people and injured more than 500 others. It was Japan's worst train wreck since 1963.