A stampede at a campaign rally for Yemeni President Ali Saleh left 51 people killed and 238 others injured in the southern province of Ibb, police and medical sources said.
Most of the injured were treated at hospitals and released, the official Saba news agency reported.
Tens of thousands attended the rally to hear an address by Saleh, who is seeking a new seven-year term in presidential elections scheduled for September 20.
The crush began when thousands of people, who arrived from mountain villages outlying the city of Ibb, tried to force their way into a stadium as thousands of other people were leaving the rally.
"The rally was over, and people who came late from remote villages wanted to enter while tens of thousands were leaving the stadium," said Mohammed Hussein, a teacher who attended the rally.
Other witnesses said a platform where top government officials were seated collapsed as people tried to escape the panicked crowd, aggravating the situation.
They said the officials in attendance had left the stadium shortly before the platform collapsed.
Streets around the stadium and across the mountainous city were blocked by thousands of cars that carried Saleh's supporters to the rally, a police official said.