An "intense lockdown" to check the spread of the highly infectious coronavirus or COVID-19 began this morning in five cities of Tamil Nadu, including Chennai, that have recorded nearly half of the state's 1,821 cases. The lockdown has been intensified for four days in three cities - Chennai, Coimbatore and Madurai (till 9 pm on Wednesday). Two smaller cities - Salem and Tirupur- are under stricter restrictions for three days (till 9 pm on Tuesday).