A US city has probably become the first in the world to make health warning labels mandatory on mobiles from next year.

San Francisco has passed a legislation that could see cell phone shops in the city displaying health warning labels prominently showing the radio-wave emission levels of various different models they sell from next year, the media reported.

The law requires that mobile stores to display the Specific Absorption Rate levels -- that is the amount of radio-frequency energy absorbed by the body per unit of body mass -- of every phone either on the handset itself or on a poster within the store.

The legislation was passed despite opposition from mobile phone industry representatives, who argued the measure could be seen as supporting the view that higher emissions might be linked to health risks.

According to US Federal Communications Commission rules, cell phones cannot have a SAR greater than 1.6 watts per kilogramme.

San Francisco mayor Gavin Newsom is to sign the ruling into law after a 10-day public comment period.