At least four persons were killed in a shooting at a mall in Washington on Friday night, police said.The shooter remains at large after opening fire at Cascade Mall in Burlington, Sgt. Mark Francis said on Twitter.Francis said it was not immediately known if there was more than one gunman involved, but authorities were searching for a man wearing grey and was last seen walking toward Interstate 5 highway -- the main interstate highway on the West Coast of the US -- from the mall, NBC News reported.Francis tweeted that survivors would be transported by bus to a nearby church.Reports about the shooting started coming in around 7 p.m., Washington State Trooper spokeswoman Heather Axtman said.It was not clear how many persons were injured, Axtman added.There is no indication that the event was terror related and there is no motive at this time, according to the spokeswoman.The Cascade Mall is an enclosed shopping mall that opened in 1990. It features Macy's stores, restaurants and a movie theatre, NBC News added.