At least 71 people were killed in the attack, and at least 33 others were wounded, according to the Aden governor's office and medics.
The car bomb exploded inside a training camp for forces allied to Saudi-backed Yemeni President Abdu Rabu Mansour Hadi, according to two senior security officials in Aden.
The explosion occurred at 8:15 a.m. local time (1.15 a.m. ET) while recruits were waiting in line to be enrolled among troops heading to battle at the Saudi-Yemeni border, the officials said.
Aden has been the de-facto capital of Hadi's Saudi-backed government. The actual capital, Sanaa, has been under the control of Houthi rebels since last year.
It is the latest bloody attack in the country's civil war.
This month alone, airstrikes carried out by the Saudi-led coalition on two schools
killed 14 children. The coalition denied targeting Yemeni schools, instead insisting it aimed for a militia training camp.
Another, on a hospital
, also took 14 lives. The hospital attack prompted Doctors Without Borders to pull its staff
from six hospitals in northern Yemen. The coalition said it regretted the aid group's withdrawal from the country.
The Saudi-led coalition of several predominately Sunni Muslim Arab nations began a military campaign in Yemen in March 2015 aimed at preventing Houthi rebels allied to Iran and forces loyal to Yemen's deposed President Ali Abdullah Saleh from taking power.
Fighting began in earnest in early 2015 when the Houthis drove out Yemen's US-backed government, led by Hadi, from Sanaa.
The conflict escalated into a multisided war, allowing al Qaeda and ISIS -- other enemies of the Houthis -- to grow stronger in the country, strategically located at the opening to the Red Sea.
A ceasefire went into effect in April, but the lull in fighting was short-lived, and peace talks that started that month reached a dead end by August.