People fleeing Japan's crippled nuclear plant are being turned away from evacuation centres because of unfounded fears they might irradiate others.

Those made homeless by the emergency at the stricken Fukushima Daiichi nuclear plant need local government-issued certificates proving they are not contaminated before they are allowed inside the centres.

Screening facilities set up to soothe concerns over radiation have become checkpoints that determine access to a place to sleep and - in at least one case - healthcare, even though experts say evacuees pose no risk to others.