An overpass under construction collapsed Thursday in this World Cup host city, killing at least two people and trapping a commuter bus, two construction trucks and a car in an embarrassment for a country that has been basking in praise for what has mostly been a smoothly running soccer tournament.

At least 22 people were reported injured. There was not yet any word on whether foreign tourists were among those killed or injured.

Vehicles lay crushed beneath an overpass built for the Brazil World Cup that fell in Belo Horizonte on July 3, 2014. (Carlos Greco-DYN/Reuters)

Brazilian officials didn't think the casualty numbers would rise too sharply — though they said they had not yet reached a small passenger car that was flattened by the falling overpass. It was not known if anyone inside the car escaped or remained inside.

The incident is the biggest black eye yet for Brazil's hosting of the World Cup, which has been carried out with less chaos than many had feared.

In the run-up to the event, there were serious concerns about the ability of Brazil's airports and roads to handle the influx of tourists because of delays or outright cancellations of projects to improve urban transportation.

After Brazil was awarded the World Cup in 2007, politicians promised $8 billion would be spent on 56 airports, subway lines and other such projects nationwide. But less than 10 of the infrastructure projects were completed in time for the tournament, including the project where the overpass collapsed in Belo Horizonte.

'Like an earthquake or a bomb'

It was not known what caused the overpass to fall. Cowan, the construction company responsible for building it, said investigators were on site but had not released any conclusions.

I couldn't see anything but a huge cloud of dust. - Alexandra Pereira, witness to collapse

"It sounded like an earthquake or a bomb," said Alexandra Pereira, a teacher who was taking a nap with her 10-year-old son in her apartment building just 20 metres from the overpass. "I looked out my window and panicked. I couldn't see anything but a huge cloud of dust."

Within seconds, Pereira said, her neighbours from the ground floor rushes out to pull injured from the bus that was partially trapped under the overpass.

Pereira said she and several neighbours in a group of nine residential buildings close to the overpass had long complained to the mayor's office that they feared for their safety from the construction and asked authorities for compensation so they could move.

She said the request was rejected and the mayor's office assured them the project was safe. The mayor's office ws closed for the day, but Lt. Col. Edgar Estevo da Silva, a spokesman for the fire department, said officials had inspected the nearby apartment buildings and didn't find any sign they were at risk because of the overpass collapse.

Bus driver among dead

Among the dead was a woman who was driving a commuter bus trapped by the overpass, said Capt. Federico Pascual of the Belo Horizonte fire department. An official in the mayor's office reported the death of a second person.

The official said 22 people were known to be injured. The official spoke on condition of anonymity because he wasn't authorized to talk to the media about the incident.

The overpass collapsed about 3 miles (5 kilometres) from Mineirao stadium, which has hosted several World Cup matches in recent weeks and is the site of a semifinal match Tuesday.

The overpass "arched over a really busy thoroughfare," Pascual said.

Security camera footage showed heavy traffic on the street below the structure the moment that the overpass collapsed, striking vehicles below and trapping them underneath.