Soldiers were deployed at a shopping centre in Bulawayo's township of Entumbane where protesters looted shops.
"The main roads to town have been barricaded with rocks and there is no public transport carrying people", Phibeon Machona, a 27-year-old Epworth resident said.
"We have suffered enough", author Philani Nyoni who was part of the protest in Bulawayo.
"We want Mnangagwa to know our displeasure in his failure", said an angry Mthandazo Moyo, aged 22.
"It's tense since early morning", Nhamo Tembo, an Epworth resident said.
After years in worldwide isolation, Zimbabwe's economy has been on a downturn for more than a decade with cash shortages, high unemployment and recently a scarcity of staples such as bread and cooking oil.
The government announced an increase from $1.34 for a litre of petrol to $3.31 with diesel surging to $3.11 per litre, igniting widespread discontent.
Zimbabwe ditched its own currency after it was ravaged by hyperinflation in 2009 under former president Robert Mugabe, who was ousted by the military to pave way for Mnangagwa in November 2017.
The main labour alliance, the Zimbabwe Congress of Trade Unions (ZCTU) has called for a three-day stay-at-home strike as it said the government had shown a clear lack of empathy for the already overburdened poor.
"It has become obvious that there is deliberate plan to undermine and challenge the prevailing constitutional order", said government spokesman Nick Mangwana in a statement late Sunday night.
He accused unnamed opposition parties of disguising themselves as civic groups and of sponsoring civil unrest. Party leader Nelson Chamisa - who narrowly lost to Mnangagwa in July's disputed election - has called on the president for dialogue to find ways to resolve the country's crippling economic crisis.
Other measures which Mnangagwa announced to ease the economic pressure include what he said was "a package of measures" to cushion its workers, until a full review of cost of living adjustment package due to take effect in April in the context of the current budget.
Government doctors went on a 40-day strike in early December, demanding salaries in USA dollars and improved working conditions, while teachers' unions called a strike this week for better pay but their calls went largely unheeded.
Zimbabwe's powerful labour-union confederation called for a national strike starting at midnight after the government more than doubled fuel prices to among the highest in the world.
He claimed that some Zimbabweans were taking advantage of the fuel crisis in the country to cause instability.
Often, a government would reveal such news a week or two prior to the price increase but that was not the focal point in yesterday's news.
Mnangagwa, who has pledged to revive the moribund economy, blamed the shortfall on increased fuel usage "compounded by rampant illegal currency and fuel trading activities".