A suicide bomber in Yemen has blown himself up outside a police academy in the capital Sanaa, killing dozens of people.

Authorities have blamed the attack on Al Qaeda, which has carried out many similar attacks in Yemen before.

The bombing followed a similar attack in in May, when a suicide bomber in army uniform killed more than 90 people during a rehearsal for a military parade.

The blast happened as hundreds of police cadets were leaving the academy to head home for the weekend.

"We ran to the place and found dozens of cadets covered in blood. Blood was everywhere. The scene was horrific," police man Fadel Ali said.

One witness said the bomber arrived in a taxi which was blown to pieces in the blast, while ambulances rushed to the scene to evacuate casualties.

Another witness said he saw a man in his 20s enter the crowd as cadets gathered in front of the academy. "A loud explosion shook the area and I saw cadets lying on the ground with blood everywhere."

A police source said that the suicide bomber was not killed instantly, but died later in a police hospital.

The attacker apparently died on the way to hospital after losing several limbs.

About 4,000 cadets study at the academy.

Security officials say 11 people were arrested shortly after the attack.

No group has claimed responsibility.

ABC/Reuters