A 15-year-old girl was killed after a suspension bridge over a river collapsed.

A 15-year-old girl was killed after a suspension bridge over a river in southwest France collapsed on Monday, causing a car, a truck and possibly a third vehicle to plunge into the water, local authorities said.

Four people were rescued but several others were feared missing after the collapse of the bridge between Mirepoix-sur-Tarn and Bessieres, 30 kilometres (18 miles) north of Toulouse, said fire service and local security chief Etienne Guyot.

The central part of the 155-metre (510-foot) bridge, measuring 6.5 metres wide, was submerged by the fast-flowing Tarn river.

A car bonnet could be seen sticking out of the water as helicopters circled overhead and emergency workers in inflatable boats searched for survivors.

Over 60 emergency service members, including divers, were taking part in the rescue operation, Guyot told reporters, adding there were "probably several missing".

Among those feared missing were the truck driver and the driver of a potential third vehicle, Guyot said, adding that witnesses had reported seeing a van on the bridge.

The dead girl was travelling by car across the bridge with her mother when it collapsed.

Her body was retrieved from the river, which is 100 metres wide and over 20 metres deep at the level of the bridge.

The girl's mother was pulled alive from the sunken car by bystanders, some of whom were badly injured in the rescue attempt.

Two rescue workers were also seriously hurt, according to the region's security department.

'Important crossing point'

An investigation into the cause of the accident was underway.

The bridge, dated to 1931, had a load limit of 19 tonnes and was "regularly checked", Guyot said.

The Haute-Garonne department council said the bridge had undergone a "thorough" inspection in 2017, which had shown "no structural problem".

Mirepoix-sur-Tarn mayor Eric Oget described it as a "very important crossing point" for people going to work in the regionla capital Toulouse on the other side of the river.

Many pedestrians used the bridge, he said, describing the collapse as a "real trauma" for the local population.

Oget said articulated lorries were not allowed onto the bridge but that some had nonetheless been seen crossing over in the past.

He said he had no information on whether the fallen truck exceeded the allowed weight.

The issue of bridge safety was thrust into the spotlight in Europe after the collapse of a motorway bridge in the Italian city of Genoa in August 2018, in which 43 people died.

An audit of France's bridges commissioned by the Senate in the wake of the Genoa disaster called for major investments to avoid a similar tragedy in France.

"Unfortunately what happened illustrates what we said in the report, which is that the state of our bridges poses a real danger," senator Herve Maure, who oversaw the audit, told AFP.

"If a bridge which is not listed as dangerous collapses, what is the situation of those bridges which were clearly identified as dangerous in the report?" he said.