Fifteen people were injured in a Mishima stabbing attack at a Yokohama Rubber factory in central Japan, in one of two serious incidents reported in the country on 26 December.
A separate multi-vehicle crash on the Kanetsu Expressway in Gunma Prefecture left at least 21 people hurt.
According to police and emergency officials, the Mishima attack happened on Wednesday afternoon when a man entered the factory armed with a knife and carrying a liquid substance.
Workers contacted emergency services after several colleagues were stabbed and others complained of being sprayed with a chemical.
What happened in the Mishima stabbing attack
Authorities say eight victims suffered stab wounds and seven more were exposed to the liquid, which early reports suggest may have been a bleach-type chemical.
All 15 were taken to hospital. Initial assessments indicated that several victims were seriously hurt but none were in a critical condition.
The incident took place on the production floor of the plant, which manufactures tyres for trucks and buses. Images from the scene showed multiple ambulances and fire trucks outside the building while staff were evacuated and decontaminated as a precaution.
Police arrested a 38-year-old man at the factory on suspicion of attempted murder.
He was reported to have been wearing a gas mask and carrying a survival knife when detained.
Investigators are questioning him to establish a motive and whether any of the workers were specifically targeted.
Kanetsu Expressway crash in snowy conditions
Later that evening, emergency crews were called to a major accident on the outbound lanes of the Kanetsu Expressway near Minakami Town in Gunma Prefecture.
The crash involved at least 15 vehicles and triggered several fires.
Authorities say 21 people were injured in the pile-up. Some were treated at the scene while others were taken to nearby hospitals. No official death toll has been released.
Traffic on the affected section of the expressway was halted while firefighters extinguished burning vehicles and police began documenting the scene.
Early information from road authorities points to snow-covered, slippery conditions as a likely factor in the collision. Investigators are examining vehicle speeds, following distances and weather warnings issued for the area at the time.
Separate investigations under way
Police have indicated there is no link between the Mishima stabbing attack and the Kanetsu Expressway crash.
In Shizuoka Prefecture, detectives are gathering witness statements, reviewing security footage from inside the factory and analysing the liquid used in the assault.
In Gunma, highway patrol units and transport officials are reconstructing the sequence of impacts on the expressway and checking whether any additional safety measures are needed on the busy holiday route.
Both investigations are ongoing, and authorities have not yet announced when further updates will be provided.
