WINTER PARK, Colo.--A huge boulder dislodged by a state highway worker rolled off a mountainside yesterday and smashed into a moving sightseeing bus, killing seven people and injuring 15 others, authorities said.

Dan Hopkins, spokesman for the Colorado Highway Department, said a crew was clearing rock above the roadway and that a front-end loader dislodged a large rock.

The worker had pushed the boulder onto a large flat area, he said, adding that "the crew was operating under the plan that the rock would hit and stay there."

However, "the rock proceeded over the edge of the large flat area down through several hundred feet of trees onto the highway below, where it collided with the bus," Hopkins had said earlier in a prepared statement.

The highway department is investigating the accident, but Hopkins said he did not know whether any disciplinary action was planned against the equipment operator.

"It's a terrible accident," Gov. Roy Romer told reporters at a news conference last night. "Quite frankly, it's our responsibility to make it right."

Romer said he is less concerned at this point about determining liability than aiding the victims and their families. The state will pay medical costs for the injured, help bring family members to Colorado and provide counseling, he said.

"I am personally accepting responsibility for the state," he said. "We'll let the lawyers catch up with us later."

Six people died at the scene and a California woman died at a Denver hospital Monday evening. At least four other of the 28 people aboard the Gray Line tour bus were seriously injured, and eight people remained hospitalized. Only six passengers were unhurt.

"The right side of the bus was completely torn off, so the seats were completely exposed," said Teri Maddox, a reporter for the weekly Winter Park Manifest and one of the first people on the scene.

"Three bodies were on the pavement, and the rest of the people were either standing around, sitting or lying down. Most were pretty cut up, even those not injured seriously."

The victims were American and foreign tourists on a one-day sightseeing tour of the Rocky Mountains. Their names were not immediately available, but authorities said three of the dead were women and three were men.

The boulder, which authorities said weighed several tons and measured 17 feet across and 6 feet high, struck the Gray Line tour bus just before 11 a.m. as it neared the foot of the heavily traveled 11,314-foothigh Berthoud Pass on U.S. 40. The accident site is about 60 miles northwest of Denver.