Four people were killed in a stampede at an open-air New Year concert in Banjul on Thursday, police said.Thousands of people had gathered for the free entertainment, sponsored by a mobile phone company, when there was a "big stampede", police spokesman Assistant Superintendant Sulayman Secka said on state television late on Thursday. One man and three women, including one from Sierra Leone were killed, he said. "For the time being we are investigating ... the cause of the stampede," Secka said.