HARARE, Zimbabwe — Police stormed the main opposition party headquarters yesterday and arrested its leader shortly before President Mugabe left for an emergency meeting of southern African leaders about the crisis in Zimbabwe.

Morgan Tsvangirai and other Mugabe opponents were taken into custody hours before the opposition leader planned to talk to reporters about a wave of political violence that left him briefly hospitalized.

Police sealed off approaches to the Movement for Democratic Change headquarters and fired tear gas to drive away onlookers before taking Mr. Tsvangirai and the others away in a bus, said Eliphas Mukonoweshuro, an aide to Mr. Tsvangirai.

“We don’t know their whereabouts. We don’t know if they have been charged,” he said.

State radio said Mr. Mugabe left for Tanzania to attend a meeting of the Southern African Development Community on the political turmoil in Zimbabwe amid concerns the crisis could threaten regional stability.

Before leaving, Mr. Mugabe held a meeting of his politburo, the ruling party’s highest policy-making body, to discuss whether to hold national elections in 2008 or 2010.

Ruling party spokesman Nathan Shamuyarira said Mr. Mugabe, who has pushed for a delay until 2010 that would lengthen his rule, expressed willingness to contest the elections if nominated.

The radio report said the party would go ahead with elections regardless of whether the opposition takes part. On Tuesday, Mr. Tsvangirai said he would boycott a presidential election scheduled for next year unless it was carried out under a new democratic constitution that ensures it is free and fair.

Mr. Mugabe is under growing pressure to step down as leader of the country he has ruled since independence in 1980. Tensions are said to be rising in his party over his succession, and the opposition blames him for the country’s corruption and acute shortages of food, hard currency, and gasoline.

But the 83-year-old leader has denied his rule is nearing an end and has vowed to crush opposition to him and his government.

Mr. Shamuyarira told state radio Mr. Mugabe would brief the Tanzania meeting about violence in the country and the arrests of activists.

Mr. Tsvangirai, 54, was arrested along with about 50 other people on March 11 as opposition, church, student, and civic groups tried to stage a prayer meeting. His supporters said police smashed his head against a wall repeatedly.

The European Union said it viewed yesterday’s arrest of Mr. Tsvangirai with “great concern,” said Jens Ploetner, a spokesman for the Foreign Ministry of E.U. president Germany.

“The E.U. president holds the leadership of Zimbabwe responsible for the bodily injury to Mr. Tsvangirai and calls for him to have immediate access to legal, and if necessary, medical consultation,” Mr. Ploetner said.

The international human rights group, Human Rights Watch, called on the meeting of regional powers to take strong measures to address the escalating crisis.

It said in a statement that the Zimbabwean government has permitted security forces to commit serious abuses with impunity against opposition activists.