The final entry in Michael and Johnny Mak's Long Arm of the Law series, Underground Express once again tells a story of gangsters versus police, focusing on the difference between how both factions act depending if they're coming from Hong Kong or Mainland China.
| Release Date | June 5, 1990 | |
|---|---|---|
| Status | Released | |
| Original Title | 省港旗兵第四集:地下通道 | |
| Runtime | 1h 40min | |
| Budget | — | |
| Revenue | — | |
| Language | Cantonese | |
| Original Language | cn | |
| Production Countries | Hong Kong | |
| Production Companies | Johnny Mak Production Co. Ltd. | |