Bodies lapped at the shoreline of the island of Utoya, while the injured screamed, helicopters buzzed overhead and dozens of ambulances waited at the shore, witnesses said after the shooting at a youth conference in northern Norway.

Andre Skeie, 26, who lives near the island, was one of about 20 people who answered a police call for those with boats to come and help the rescue effort.

In a telephone interview, he said he and his friends left the small town of Honefoss, drove to shore and took their boats out to the island, where they saw about 50 people standing near the water, many of them severely wounded.

“It was like a war zone,” he said. “You could see badly injured people. Some of the people didn’t have a face. The injuries were so bad that [the gunman] must have used a large-caliber weapon.”

Norwegian police said early Saturday that at least 80 people had been killed in the shootings. Skeie said that, as the boats approached the island, he counted 17 to 25 bodies in the water, although initially he did not realize what the floating objects were.

He said the victims must have been running away and jumping in the water. But some had bled to death, and their injuries were so bad he assumed they had been shot in the water.

“We picked up the injured people,” Skeie said, “and they were all in shock and they were crying and screaming. The boat was covered in blood.”

Some victims were badly wounded in the stomach and the arms. He took about 15 to shore, and ferried doctors back to the island on his return trip.

There were about 700 people at the camp, he estimated, and most of the victims were between ages 16 and 25.

“I don’t feel anything right now. . . . So many people my age, it’s difficult to understand what happened,” he said from his home, where he was watching the news with his friends.

Hanne Sommerstad, 50, who was vacationing with her family in a summer cottage on the island of Storoya, a few hundred yards away, said helicopters were still overhead at 11 p.m., shining spotlights into the sea.

“I feel shocked to think this is happening in Norway on a little calm island,” she said. “We are not used to these terror things in Norway. It’s very unreal. We can’t believe this.”

In Oslo, Labor Party members were rocked by the news. Bjorn Tore Hansen, a communications secretary with the party, was outside central Oslo when the explosion shook the city in the afternoon.

Relieved no one from his office was injured, he was following the situation on Twitter when a friend at the camp called.

“He said, ‘There’s shooting,’ ” said Hansen, 27. At first, he didn’t believe his friend, but then he saw that some of his nearly 100 friends who were at the camp were tweeting about a gunman.

“I was shocked,” he said in an interview. “Attacking the government is one thing, but attacking innocent youth at a political camp, that’s beyond horrible and ten thousand times worse than attacking government buildings, attacking defenseless children.”

“A lot of people are in the hospital now, and a lot are still missing,” he added.

Like his friends, Hansen said that he would spend the night on Facebook, where young people have been leaving messages of support, changing their profile pictures to Norwegian flags and updating their statuses to let people know they are safe.

“It’s a relief to see every single person I know that is still alive,” Hansen said.