Story highlights Two police helicopters crash in Berlin

The pilot of one helicopter died

Two other people were severely injured, police say

A helicopter pilot died after two police helicopters crashed at Berlin's Olympic Stadium in Germany on Thursday, police said.

Two other people were severely injured and several others moderately or slightly injured.

Rotors of the two helicopters apparently hit each other as they were landing, federal police spokesman Meik Gauer said.

The cause of the crash, which happened about 10:15 a.m. (5:15 a.m. ET), is not yet known, police said.