At least 15 people have died as the bus they were travelling in overturned in northeastern Brazil, local officials have said. The vehicle had been carrying about 60 people who were returning from a pilgrimage when it crashed on a curved stretch of a highway in the rural interior of Alagoas state on Tuesday morning.

Three children were among those who died, a statement said, while some surviving passengers were airlifted to hospital for treatment.

Footage on social media shows a bus turned on its side, with debris surrounding it and emergency crews at the scene. An investigation has been launched. Authorities said they believed that the driver had lost control of the bus before it left the highway and rolled over several times.

According to media reports, the most seriously injured patient transferred to hospital was a nine-year-old child who suffered a head injury. The passengers were taking part in the pilgrimage of Our Lady of Candeias, a religious festival in the state of Ceará.

The bus was part of a convoy carrying hundreds of people from the city of Coité do Noia in Alagoas to Juazeiro do Norte in Ceará, a journey spanning 563km (350 miles) which normally takes around eight hours.

The incident happened in São José da Tapera on the final stretch of the journey back to Coité do Noia. Bueno Higino Filho, mayor of Coité do Noia, told local media: 'The loss is immense. They were all my friends... I woke up today to the sad news and I'm heading to the site of the accident to see what we can do [to help].'

Three days of mourning have been declared by the governor of Alagoas state. 'I stand in solidarity with the family members and friends in this moment of such great pain,' Paulo Dantas wrote on social media.