Change row value of dataframe column with sequence number

Question

I have huge a dataframe with thousands of rows and unique name of the area maybe a hundred areas. My data looks like this:

df
    Area
0   A Area
1   B Area
2   C Area
3   A Area
4   D Area
5   E Area
6   B Area
7   C Area
8   D Area
9   A Area
10  A Area
11  B Area
12  B Area
13  E Area
14  F Area
.............

I want to make a new column included a code in every unique area with a sequence number. How to execute automatically in pandas with unique in column area maybe hundred or thousand. My expected result looks like this:

Result
    Area    Code_district
0   A Area  district-1
1   B Area  district-2
2   C Area  district-3
3   A Area  district-1
4   D Area  district-4
5   E Area  district-5
6   B Area  district-2
7   C Area  district-3
8   D Area  district-4
9   A Area  district-1
10  A Area  district-1
11  B Area  district-2
12  B Area  district-2
13  E Area  district-5
14  F Area  district-6
...........