Try adding the -y switch (assume Yes on all queries)
Or try to redirect the output content to a file:
cmd /c "C:\\Program Files\\7-Zip\\7z.exe" x Src.7z -oD:\\tmp -r -y > out.txt
Note: sometimes the problems with calling processes is that you need to process / clear the output the produce. once their output buffer is full, they wait for the buffer to come free again.