US police have captured an ethnic Chechen teenager suspected of staging the Boston Marathon bombings, after a desperate manhunt that virtually paralyzed the city and its suburbs.
Responding to a tip from a local resident, police found Dzhokhar Tsarnaev, 19, hiding in a boat in a suburban backyard in Watertown, wounded and weary after a gun battle overnight in which his accomplice brother was killed.
"Captured!!! The hunt is over. The search is done. The terror is over. And justice has won. Suspect in custody," the Boston police department said on Twitter after Tsarnaev was taken away to applause from relieved residents.
Hundreds of people later descended into the streets of Boston to celebrate, chanting: "USA! USA!" Some climbed onto car roofs while others danced in the streets.
A neighbor alerted police after finding Tsarnaev "covered with blood" in the boat where he had taken refuge, Boston police chief Ed Davis told reporters.
The University of Massachusetts student was surrounded by a small army of police for a final showdown which lasted nearly two hours. Attempts to negotiate with him failed as he was "not communicating," Davis said.
"We exchanged gunfire with the suspect who was inside the boat, and ultimately, the hostage rescue team of the FBI made an entry into the boat and removed the suspect," Davis told a press conference.
Following his capture, Tsarnaev was taken to hospital, where he was in serious condition.
"We will determine what happened. We will investigate any associations that these terrorists may have had. And we'll continue to do whatever we have to do to keep our people safe," President Barack Obama said after the capture.
It was not immediately clear when Tsarnaev would be formally charged. US Attorney Carmen Ortiz declined to comment on possible charges he would face, saying the investigation was ongoing.
The arrest ended a dramatic four days after two bombs exploded at the marathon finish line, killing three people and wounding about 180 in the worst attack on the United States since the September 11, 2001 terror attacks.
Dzhokhar Tsarnaev and his 26-year-old brother Tamerlan were named as the main suspects. They were also at the center of a violent spree in which one policeman was killed and a second officer wounded.
Investigators at first struggled to identify the attackers, but a major breakthrough came when the Federal Bureau of Investigation on Thursday released video and picture images of the Tsarnaev brothers as they walked in Boylston Street where the attacks took place.
Within hours of that press conference, the brothers embarked on a final rampage through the Boston suburbs.
A police officer was killed in a "vicious assassination," Davis said, and the suspects then carjacked a Mercedes, sparking a high-speed police chase to Watertown.
Police said the two men hurled explosives out of the car window before the elder brother was shot. Tamerlan Tsarnaev died of bullet wounds and injuries from explosives strapped to his body, a hospital doctor said.
Police launched a huge manhunt on Friday with 9,000 police surrounding Watertown and parts of nearby districts hoping to isolate the teenager, who was believed wounded in the shootout in which his brother was killed.
Boston ground to a standstill as authorities halted all public transport, ordered schools and universities closed and told people in most of the region to stay in their homes.
The Tsarnaev brothers are ethnic Chechen Muslims who moved to the United States about a decade ago.
Their social media pages appeared to express sympathy with the struggle of Chechnya, which has been ravaged by two wars since 1994 between Russia and increasingly Islamist-leaning separatist rebels.
The suspects' father Anzor Tsarnaev told Russia's Interfax news agency his sons had been "set up by the secret services because they are practicing Muslims." But an uncle, Ruslan Tsarni said the pair had put "shame on the entire Chechen ethnicity."
"Somebody radicalized them," he said of his nephews. "It's not my brother."
The FBI acknowledged on Friday that an unnamed foreign government had asked about Tamerlan Tsarnaev in 2011 but they had found no key information.
Obama said the bombing suspects had failed to achieve whatever it was they were seeking.
"They failed because the people of Boston refused to be intimidated," he said. "They failed because as Americans, we refuse to be terrorized."
Boston has held emotional tributes to the dead -- eight-year-old Martin Richard, Boston University graduate student Lu Lingzi of China and Krystle Campbell, a restaurant manager.
More than 100 of the wounded have left Boston hospitals and fewer than 10 remain in critical condition.