UPDATE 6:40 a.m. EST:
The death toll in the attack has risen to 59, with at least 117 people wounded, according to the Associated Press.
The Islamic State claimed responsibility for the attack, but that has not been verified. The Hakimullah group, a breakaway faction of the Pakistani Taliban, also claimed responsibility, which could not be confirmed.
At least 20 people were killed and dozens were injured late Monday when gunmen stormed a police training center in the city of Quetta, Pakistani officials told Al Jazeera.
Officials said the gunmen attacked a center where approximately 500 cadets were staying.
"At least 20 were killed but this figure isn't final -- we'll confirm in the morning," the home minister of the Balochistan province told reporters.
The number of attackers remains unclear, although officials believe there were at least five initially. Two attackers were reportedly killed, according to the BBC.
However, security forces told Al Jazeera that there were four attackers and they were all killed while exchanging fire with troops.
Hundreds of police trainees were evacuated from Balochistan Police College as troops worked to stop the militants.
This isn't the first time the facility has come under attack. Rockets were fired at the facility in 2006 and 2008, according to Al Jazeera.
In August, 88 people were killed in Quetta in attacks targeting a hospital and lawyers in the region.