A report in the state-run Bulawayo Chronicle newspaper said those arrested had been protesting over what they said was the unfair distribution of food.
"
We have had enough of this - we are starving while some people have plenty of maize
"
Bulawayo resident
The state-run Zimbabwe Broadcasting Corporation reported that residents had accused grain board officials of corruptly supplying maize to unscrupulous millers, who then sold it on at exorbitant prices.
Correspondents say that millions of people in Zimbabwe are threatened by famine as the result of the continuing drought and the disruption caused by government's seizure of white-owned farms.
Favouritism
Maize meal, the national staple food, is supposed to be sold at controlled prices, but there have been reports that some millers are trying to evade the price controls.
Police fired tear-gas at the crowds and charged them with batons to try to quell the violence, witnesses said.
The privately-run Daily News said that about 4,000 people had been queuing at the depot on Friday when the fighting began.
The violence was said to be the most severe since food shortages began but no injuries were reported.
Some witnesses said the rioting had started because supporters of President Mugabe's Zanu-PF party were getting preferential treatment at the grain distribution centres.
"We have had enough of this. We are starving while some people have plenty of maize," the Daily News quoted one demonstrator as saying.
Full blown crisis
Correspondents have reported seeing state grain depots only selling maize to people holding party membership cards.
They say Mr Mugabe is using food as a weapon to ensure that he remains in power.
Zimbabwe is in the grips of a massive economic crisis and about eight million people are thought be under threat of famine, with the problems not just restricted to rural areas.
Opposition parties point the finger of blame at Mr Mugabe and his government, but for his part the president says the cause of the crisis is a combination of a drought and a Western imperialistic plot aimed at keeping power in the hands of Zimbabwe's whites.