- 11 May 2016
- From the section India
Twitter users have responded with hashtag #PoMoneModi (Go Off Modi) and Chief Minister Oommen Chandy said Mr Modi's remarks were "baseless".
Kerala will hold elections on 16 May.
Mr Modi's Bharatiya Janata Party (BJP) has been trying to get a foothold in the southern Indian state which has been traditionally ruled by either Congress-led governments or a coalition of left parties.
But his recent statement to win Kerala's voters seems to have backfired.
Somalia has one of the highest rates of child malnutrition and infant mortality in the world, while Kerala state has lowest infant mortality rates in India. Scheduled tribes are among India's most underprivileged citizens.
Mr Chandy on Tuesday wrote a letter to Mr Modi and sought an apology from him.
"You made statements that had nothing to do with reality and likened Kerala to Somalia. This is unbecoming of a prime minister and has created a great deal of agony," Mr Chandy wrote.
And on Wednesday, #PoMoneModi became one of the top trending topics on Twitter with people using memes, cartoons and jokes to express their anger.
Meanwhile, some users urged people to use their anger during the voting day and not insult Somalia in their tweets.
And some others defended Mr Modi.
Read more: http://www.bbc.com/news/world-asia-india-36264001