"The ban becomes effective today," said Ali Juma, semi-autonomous Zanzibar's environment chief.

"We have been lax in the implementation of the environment laws, but it is a fact that plastic bags are very dangerous to land and damaging to marine life," he told reporters.

The regulation bars the importation, distribution and sale of light plastic bags whose thickness is measured at 30 microns and below and follows similar moves by countries on the African mainland.

Zanzibari offenders of the law risk jail sentences of six months, a fine of up to 2,000 dollars (1,560 euros) or both.

Juma said his office would begin an islands-wide awareness campaign to educate Zanzibaris about the dangers of the flimsy shopping bags, which, when discarded in the open, can pose significant threats to humans and animals.

Experts say the bags can provide micro-habitats for malaria-carrying mosquitos, block gutters and drains, choke farm animals and marine life, pollute the soil, are visual blots and can take 20 to 1,000 years to decompose.

Enforcement of the ban on Zanzibar comes as authorities seek to improve environmental protection on the islands, world renowned for their exotic spice- and slave-trade history as well as pristine, palm-fringed beaches.

Last month, officials warned that Zanzibar was in danger of becoming one of the world's most environmentally endangered island chains due to unchecked disposals of raw sewage, solid waste and deforestation.

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