Police have prevented protesters reaching central Harare
Zimbabwean police have fired warning shots and tear gas to disperse crowds gathering at the start of a week of protests against President Robert Mugabe's government.
The mass action is designed to drive Mr Mugabe from power, called by the opposition Movement for Democratic Change.
The authorities have declared the protests illegal and warned that anyone taking part in them will "face the full wrath of the law".
At least one person has been shot, and an AFP news agency reporter has described how police rounded up protesters and beat them with batons.
But police spokesman Wayne Bvudzijena told the BBC Focus on Africa programme that he had not recieved many reports of violence.
The BBC's Barnaby Philips, reporting from neighbouring South Africa because of restrictions on foreign journalists, says that the week marks a defining moment in Zimbabwe's history.
He says that if the demonstrations fail, President Mugabe may feel encouraged to cling on to power, but if they succeed he will come under even greater pressure to resign.
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Earlier on Monday, MDC leader Morgan Tsvangirai was charged with contempt of court after being arrested at his home.
Mr Tsvangirai was picked up at his house and held at a police station in Harare for several hours before being charged and released.
The MDC says that its activists, including several MPs, have been arrested in Masvingo and Victoria Falls, as well as Harare and Bulawayo.
AFP also reports that pro-Mugabe militants have brutally assaulted an unamed person on the steps of a five-star hotel, before attacking cars belonging to white people.
The centre of Harare is reported to be completely shut down, with shops and factories closed.
Our correspondent says many people are presumably observing the opposition call for a stayaway, but it may be that other people are unable or too afraid to come to work.
Witnesses at the university campus in Harare saw Zimbabwean soldiers whipping students as they lay on the ground, our correspondent adds.
Leonard Chigwagwi is carried by a colleague after being shot
There are also reports of skirmishes between protestors and police in at least two of Harare townships.
In Highfield, police fired live rounds in the air to disperse a crowd of several hundred protesters.
In the second city, Bulawayo, police and armed troops dispersed protesters and several MDC leaders including two MPs are reported to have been arrested.
Other opposition leaders are reported to have gone into hiding.
The government has showered central Harare with leaflets urging people to ignore the opposition call for action.
Police and army patrols are out in force, with road blocks on the main routes leading into the city centre, and the roads around President Mugabe's official residence have been closed.
Mugabe denies causing the country's economic crisis
In the north of the capital, school children were seen making their way to classes, but some schools have planned to close over the next five days.
The High Court in Zimbabwe banned the protests after police filed an application saying they would undermine law and order and challenge the country's constitutional democracy.
At the weekend, people were panic-buying in preparation for the demonstrations.
In Harare, shoppers stocked up on essentials while thousands queued up at banks to withdraw cash.
The ruling Zanu-PF's chief spokesman Nathan Shamuyarira has said the time has come for a showdown with the MDC and that they must be "confronted and taught a lesson".
Zimbabwe is in a severe economic crisis, with record inflation and unemployment, and shortages of food, fuel and foreign currency.
President Mugabe, in power since the country gained independence from Britain in 1980, blames the crisis on opponents of his seizures of land from the white minority for redistribution among landless blacks.
Zimbabwe is under sanctions from the European Union, the United States and the Commonwealth over alleged vote-rigging by the ruling party in last year's presidential elections.