Thanks to contrinutions from Pengfei Li you can now combine maps.

library(echarts4r)
library(echarts4r.maps)

maps <- c("China","Japan") 

e_charts() %>% 
  em_maps(maps, "myMap") %>% 
  e_map(map = "myMap")

You are not limited to two maps.

maps <- c("China","Japan", "India") 

e_charts() %>% 
  em_maps(maps, "maps3") %>% 
  e_geo(map = "maps3")