(CNN) -- Four people, including two children, died when a plane crashed into a building at a hospital complex in Watsonville, California, the National Transportation Safety Board confirmed Friday.

The plane came down Thursday night in a parking lot before skidding into an office building at Watsonville Community Hospital, said Watsonville Deputy Police Chief Rudy Escalante. There were no survivors.

Authorities quickly extinguished the resulting fire at the hospital and the facility was not evacuated, police said.

"No one on the ground was injured because the physicians' offices were closed for the day," said hospital spokeswoman Cindy Weigelt.

NTSB investigator Michael Huhn told reporters Friday that investigators are on site to help determine what happened.

They plan to move the wreckage to a storage facility soon so they can evaluate it within a controlled environment, he said.

Huhn declined to identify the victims and would not speculate on what could have caused the crash.

"We're at the very beginning of the investigation," he said. "We're gathering the facts."

CNN's Amanda Watts contributed to this report.