An ammunition dump on the outskirts of the Tanzanian city of Dar es Salaam has exploded killing at least three people.
The BBC’s Vicky Ntetema in Dar es Salaam says hundreds of people have been injured as they fled in panic.
Police say several buildings in the area were set alight by debris from the blasts at Mbagala army base.
Shockwaves from at least three explosion were felt throughout the city where the authorities advised workers to vacate their offices.
Many feared a repeat of the deadly bombing linked to al-Qaeda that rocked the country’s main commercial centre in 1998.
Polycalypo Makunja was on his way to a market three kilometres away when the explosions began.
“The first thing I did was run. Everybody around me was running away,” he told the BBC News website.
“I passed people with injuries – broken arms, bleeding heads. Fires were burning. It was very bad.”
The armoury next to the army camp, which lies 14km (nine miles) outside the city centre, is thought to have contained large amounts of ordnance, including mines and artillery shells.
Our correspondent says nearby Temeke hospital is overwhelmed with casualties and the death toll is expected to rise.
The area affected by the raining debris is large, she says.
She said she saw bomb fragments and the body of a person killed by shrapnel about 15km from army base.
Near the scene of the blast, senior police officer Paul Chagonja told the BBC’s Focus on Africa programme they had received an unconfirmed report some children had drowned after jumping in a river while fleeing in the panic after the blast.
He said that a number of houses in the area had been damaged in the explosions.
“Most of them have developed very, very big cracks and some slums have collapsed,” he said.
The BBC’s John Ngahyoma in the city centre says the blast caused a tremor which was felt at the BBC’s offices near the harbour.
Several BBC News website readers in Dar es Salaam said the blast reminded them of the bombing nearly 11 years ago.
“This brought back memories of the US embassy explosion in ’98. It felt exactly the same way,” e-mailed Ahmad, who was 40km (25 miles) from the site of the ammunition dump.
Others said it seemed like an earthquake.
“It was so powerful that our building shook and the windows were forced open by the impact,” wrote Nipun from the city centre.
“We all stood still for a while wondering if it was an earthquake or something else.”
Deputy Minister for Defence and Security Emmanuel Nchimbi has cautioned residents to stay away from the area and to vacate all tall buildings as a precautionary measure.
Residents say the evacuation has lead to deadlocked streets.
“The city is in complete chaos as all persons in skyscrapers and other tall building have been ordered to evacuate causing huge traffic jams and confusion,” Niklas Rogers told the BBC.
Other Dar es Salaam residents told the BBC there is a school in the area of the explosion.
“They are told to evacuate, [but] the confusion is for those who don’t know where their children are,” said Henry Amos Tandau.