Tel Aviv was part of Jaffa at first , but it became a separate town in 1921 . On May 1 , 1921 , the Jaffa Riots erupted and an Arab mob killed dozens of Jewish residents . In the wake of this violence , many Jews left Jaffa for Tel Aviv , increasing the population of Tel Aviv from 2,000 in 1920 to around 34,000 by 1925 .