A suicide bomber driving a minibus full of explosives killed at least 30 people near a police academy in the heart of Yemen's capital, Sanaa.
The blast wounded at least 40 people, security officials said.
No one immediately claimed responsibility for the attack. Yemen's local al Qaida branch, targeted in frequent US drone strikes in the country, has carried out similar attacks in the past.
Washington considers al Qaida in Yemen to be the world's most dangerous branch of the terror network as it has been linked to several failed attacks on the US homeland.
The blast comes after Shiite rebels known as Houthis seized large areas of Yemen, including Sanaa, earlier this year as part of a protracted power struggle with President Abed Rabbo Mansour Hadi.
Their critics view them as a proxy for Shiite Iran, charges the rebels deny. Al Qaida militants have targeted the rebels in bombings in the past.
An al Qaida suicide bomber killed at least 24 people on December 31 in an attack on Houthis as they commemorated the birth of the Prophet Muhammad.