A mid-air collision of two medical helicopters left at least seven people dead and three others seriously injured Sunday in Arizona, said the Federal Aviation Administration (FAA).

A mid-air collision of two medical helicopters left at least seven people dead and three others seriously injured Sunday in Arizona, said the Federal Aviation Administration (FAA).

WASHINGTON, June 29 (Xinhua) -- A mid-air collision of two medical helicopters left at least seven people dead and three others seriously injured Sunday in Arizona, said the Federal Aviation Administration (FAA).

All three people on one of the choppers were killed, according to a FAA statement.

Among seven people on the other chopper, four were killed and three injured.

The identities of the victims are not released yet and the cause of the collision is under investigation.

This is the second plane crash in the United States Sunday.

Another single-engine small plane crashed outside of Las Vegas, Nevada, in the early afternoon, killing all four people on board.