Police in Tokyo have arrested four Vietnamese for failing to assist a fellow Vietnamese woman who died after taking illegal drugs.

Police say the four individuals and the 23-year-old woman took the synthetic drug MDMA at an eatery in Bunkyo Ward in May.

The woman showed symptoms of acute drug poisoning, but the four failed to immediately call an ambulance.

The four said they took the woman outside because she was screaming and acting violently, and put a wet towel in her mouth so she wouldn't bite her tongue.

They finally called an ambulance about 40 minutes later, after being persuaded by staff at the eatery.

But when the emergency team arrived, the woman was already unconscious and died a short while later. The four individuals had left the scene.

Police have not disclosed whether the four have admitted to charges of negligence resulting in death. Police say the four said they feared their use of illegal drugs would come to light if they called an ambulance.