HARARE, Jan 23 (Reuters) - Police took away Zimbabwe's main opposition leader Morgan Tsvangirai in the middle of the night for questioning about a demonstration planned for later on Wednesday, his lawyer said.

"The police are saying they want to know what he is planning to do today," lawyer Alec Muchadehama told Reuters by telephone.

Tsvangirai's Movement for Democratic Change (MDC) planned the march to press veteran President Robert Mugabe for a new constitution to guarantee parliamentary and presidential elections due in March are free and fair.

The MDC launched a legal challenge on Tuesday to a police ban on the march.

MDC secretary-general Tendai Biti told Reuters that Tsvangirai was picked up from his home in a suburb of the capital Harare by plain-clothes officers.

"He was picked up at around 4 a.m. (0200 GMT) in respect of the intended demonstration. His mobile phone is now off and we are really worried," he said.

The lawyer said police also detained another MDC leader, Dennis Murira.

Mugabe has been in power since independence from Britain in 1980.

Tsvangirai was last arrested in March 2007 along with dozens of opposition officials ahead of another planned march. He says police beat him up in custody. They deny this.

The police had initially granted permission for this Wednesday's march, which the MDC called to protest against a crumbling economy blamed on government mismanagement as well as to press for a new constitution.

On Tuesday, lawyer Muchadehama said the Harare magistrate's court would hear an application on Wednesday on overturning the ban, which police say was prompted by fears the demonstration would degenerate into violence and looting.

Zimbabweans have tended to shy away from demonstrations in recent years, mainly from fear of a heavy-handed response by security forces. (Reporting by MacDonald Dzirutwe, written by Richard Meares)

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