One of the most brazen terror attacks and hostage standoffs the world has ever seen played out on Tuesday into Wednesday. The shocking incident in Pakistan's restive southwestern region involved a separatist Islamist group attacking and taking control of a large passenger train.

Some 450 passengers were travelling on the train from Quetta to Peshawar when it was attacked Tuesday by militants of the outlawed Balochistan Liberation Army (BLA). The group took a number of hostages after halting the train. Many bystanders are still missing.

Soon after the train had entered a tunnel, "intense gunfire" was unleashed by the militants. There had actually ben over 100 passengers on the train who were members of Pakistani security forces, but it's unclear whether many of these personnel were armed at the time.

One eyewitness who was able to escape the mayhem, Muhammad Ashraf, described to BBC: "There was a lot of fear among the passengers. It was a scene of doomsday."

Pakistani special forces were among the first to respond to the scene, also amid helicopter cover overhead, and a shootout ensued. But it ended in tragedy. While at least 35 militants were killed, some 100 civilians were reportedly executed by the terrorists.

The hunt for the remaining attackers appears to still be ongoing, as many of the gunmen fled into the nearby mountains.

According to more details from the scene:

Pakistani forces have freed the remaining passengers from a train that was hijacked by separatist militants, security officials said Wednesday, after militants in explosive-filled vests took hundreds of people hostage and executed 100 more.

"All innocent hostages have been safely rescued, and their evacuation is underway," the Pakistani army said in a statement. late Wednesday. 

The dramatic rescue operation came hours after militants said they had executed 50 hostages, in addition to the 10 they killed late Tuesday, the 10 Pakistani soldiers they killed during a firefight on and the 30 people who they killed "in combat" on the same day.

The Pakistani army said that it rescued some 178 hostages Wednesday in addition to the 168 it recovered Tuesday.

The escaping BLA members managed to take some of the hostages with them. "Security forces say they have deployed hundreds of troops to rescue the remaining passengers. Authorities have also deployed helicopters and special forces personnel," BBC reports. 

The BLA has warned it could start executing more hostages if they are pursued, and have described "severe consequences" if further efforts are made by the government to rescue the hostages. The rough-terrain, restive region has long been a battleground of frequent terror attacks targeting Pakistan government sites and civilian targets, including random recent attacks against cars on area highways. It remains one of the world's most dangerous regions.