Dallas – At least two snipers opened fire on police officers in Dallas on Thursday night, killing four officers and injuring seven others during protests over two recent fatal police shootings of black men, police said.Dallas Police Chief David Brown told reporters the snipers fired "ambush style" upon the officers. Mayor Mike Rawlings said one member of the public was wounded in the gunfire.Police later said in a statement that a suspect is in custody and a "person of interest" had surrendered. They said a suspicious package was being secured by a bomb squad.The gunfire broke out around 20:45 on Thursday while hundreds of people were gathered to protest fatal police shootings this week in Baton Rouge, Louisiana, and suburban St. Paul, Minnesota.The protests in Dallas were among several across the country that were held after a Minnesota officer on Wednesday fatally shot Philando Castile while he was in a car with a woman and a child in a St Paul suburb.The aftermath of the shooting was live-streamed in a widely shared Facebook video. A day earlier, Alton Sterling was shot in Louisiana after being pinned to the pavement by two white officers. That, too, was captured on a mobile phone video.Video footage from the scene showed that protesters were marching along a street in downtown, about half a mile from City Hall, when the shots erupted and the crowd scattered, seeking cover.Brown said that it appeared the shooters "planned to injure and kill as many officers as they could".Search for shootersTexas Governor Greg Abbott released a statement saying he has directed the Texas Department of Public Safety director to offer "whatever assistance the City of Dallas needs at this time"."In times like this we must remember – and emphasise – the importance of uniting as Americans," Abbott said.Police arrest man as they look for suspects in #Dallasshooting https://t.co/tftqixUSKx https://t.co/fLXfAFG5i8 pic.twitter.com/3Z4y11CKgJ— RT (@RT_com) July 8, 2016The search for the shooters stretched throughout downtown, an area of hotels, restaurants, businesses and some residential apartments. The scene was chaotic, with helicopters hovering overhead and officers with automatic rifles on the street corners."Everyone just started running," Devante Odom, 21, told The Dallas Morning News. "We lost touch with two of our friends just trying to get out of there."Carlos Harris, who lives downtown, told the newspaper that the shooters "were strategic. It was tap tap pause. Tap tap pause."Demonstrator Brittaney Peete told The Associated Press that she didn't hear the gunshots, but she "saw people rushing back toward me saying there was an active shooter". Peete said she saw a woman trip and nearly get trampled.Lynn Mays was at the scene when the shooting started. He said an officer saved his life. pic.twitter.com/Kc4aXlg9GT— Caleb Downs (@Calebjdowns) July 8, 2016Other protests across the US on Thursday were peaceful. In midtown Manhattan, protesters first gathered in Union Square Park where they chanted "The people united, never be divided!" and "What do we want? Justice. When do we want it? Now!"In Minnesota, where Castile was shot, hundreds of protesters marched in the rain from a vigil to the governor's official residence. Protesters also marched in Atlanta, Chicago and Philadelphia.