At least two people are confirmed dead from the collapse, which occurred late Sunday on the Juscelino Kubitschek de Oliveira bridge linking the states of Maranhao and Tocantins.
When a section of the bridge went down, it took with it two cars, two motorbikes, and four trucks -- two of which were carrying sulphuric acid, a police spokesman told AFP.
Their dangerous cargo prompted officials to pause the search operation early Monday.
Water supplies to communities in the region were also suspended because of the possible "toxic" acid pollution, the spokesman said.
The bridge, more than half a kilometer (1,600 feet) long, spans the Tocantins River between the towns of Estreito and Aguiarnopolis and serves as the main route linking the two Brazilian states.
Brazil's infrastructure and transport department said the causes of the collapse of the bridge, which was built in the 1970s, were being investigated. It said the central beam of the structure gave way.
The collapse came on top of two other deadly transport accidents in Brazil over the weekend.
The country's worst highway accident in 17 years happened on Saturday when a bus crashed and caught on fire, killing 41 people in the southeast state of Minas Gerais.
Police said a large block of granite apparently fell from a truck coming the opposite way, striking the bus. The truck driver -- whose license was suspended two years ago -- fled the scene.
On Sunday, a private plane crashed into the city of Gramado in south Brazil, killing a family of 10 on board.
The Piper Cheyenne 400 turboprop was being piloted by a businessman named Luiz Claudio Salgueiro Galeazzi.
At least 17 people on the ground were injured, as the plane hit a building's chimney, a house and a furniture store as it crashed shortly after takeoff.
