At least 37 people have been killed and 66 others injured by a bomb blast outside a police academy in Yemen's capital, Sanaa, police say.
Two men were seen getting out of a minibus and walking away shortly before it exploded beside dozens of people queuing to enrol at the academy.
Afterwards, body parts and debris from the bus were strewn across the street.
There has so far been no claim of responsibility, but an offshoot of al-Qaeda has carried out similar attacks.
Yemen has experienced a wave of violence in recent months, with militants from al-Qaeda in the Arabian Peninsula (AQAP) battling Shia Houthi rebels who have taken control of the capital.
Wednesday's bombing took place early in the morning in a central part of Sanaa near the central bank and the defence ministry building.
The explosion was heard across the city and a large plume of smoke was seen rising from the scene.
The victims included many cadets at the police academy as well those waiting to enrol, and passers-by, officials said.
"We were all gathering and... [the minibus] exploded right next to all of the police college classmates," Jamil al-Khaleedi told the Associated Press. "It went off among all of them."
A paramedic at the scene described the situation as "catastrophic".
"We arrived to find bodies piled on top of each other," he told Reuters news agency.
Some initial reports said the attack was a suicide bombing.
But police spokesman Brig Abdul Aziz al-Qadasi told the state news agency Saba the driver of the minibus and another person were seen getting out of the vehicle and fleeing the scene before the blast.
The US embassy in Yemen condemned the attack, saying it "reveals the nihilistic vision and depravity of terror groups operating in Yemen".
Yemeni security forces personnel have been targeted many times by AQAP in the past four years. A suicide bomber killed more than 90 people in 2012 at a military parade in the capital and an assault on a military hospital a year ago left more than 50 dead.
The jihadist group has exploited the chaos and instability that has resulted from the uprising that forced longtime President Ali Abdullah Saleh from power in 2011.
His successor, Abdrabbuh Mansour Hadi, has ordered a series of military offensives on AQAP strongholds, but its members have been able to withdraw to remote, mountainous regions where they are protected by local tribes wary of the government.
President Hadi has also been weakened by the Houthi rebels from the northern province of Saada, who triggered a political crisis in September when they overran security forces in the capital and forced him to form technocratic government and reverse unpopular subsidy cuts.
The rebels were supposed to withdraw from Sanaa, but they have instead expanded their presence in central and western Yemen, triggering fierce clashes with AQAP and Sunni tribesmen.
Last week, a suicide bomb attack on Houthi supporters in Ibb left as many as 49 people dead.