US helicopters collide in mid-air

At least seven people died in a mid-air collision between two medical helicopters in the US state of Arizona, a US aviation official has said.

The incident happened close to a hospital in the city of Flagstaff.

All three people on one of the helicopters died, at least one of them a patient, the Federal Aviation Authority's Ian Gregor said.

It was not clear how many of the others who died were in the second helicopter or on the ground, he added.

Three people were critically injured in the accident, which occurred at 1545 local time (2245 GMT).