It is an election that the United States is following with great interest because it is seen as an indication of whether a left-wing candidate can win in one of the important "swing states" in the United States, where the Democrats and Republicans are evenly matched. The winner will face Republican Congressman Tom Tiffany in the midterm elections in November.
Hong has campaigned on free childcare and healthcare, among other things, but has been criticised for his previous support for cutting police funding.
Several primary elections were held in the United States overnight.
In neighbouring Minnesota, Lieutenant Governor Peggy Flanagan defeated centrist Representative Angie Craig in the Democratic primary for the Senate. This election was also marked by the struggle for power within the party between the Democrats' left and centre factions.
Meanwhile, Lisa Demuth won the Republican primary for governor of Minnesota, defeating Trump-backed candidate Mike Lindell, the man behind the pillow company MyPillow.
