More than 500,000 tweets have been sent using the hashtag #twitterisblockedinTurkey since the service was banned in the country last night, according to social media search engine Topsy.
Analysis also shows 100,000 have used the hashtag #turkeyblockedTwitter at the time of writing.
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The world's first ever 'hole in the wall' was installed in Enfield, north London, on June 27 1967.
America says it has "identified preparations" for an attack similar to that which killed at least 86, including 30 children, in April.