WEST READING, Pa. — The authorities continued to search for the cause of a powerful explosion that ripped through a chocolate factory in West Reading, Pa., on Friday, killing at least four people, sending a plume of smoke into the air and shaking houses blocks away.
At a news conference on Sunday morning, officials said that at least three people remained missing, though one person was found alive in the rubble overnight on Friday.
That discovery “provides hope that others still might be found,” said Wayne Holben, the West Reading police chief. Further details on the person’s condition on Sunday were unavailable.
The explosion, which occurred around 5 p.m., destroyed one building and damaged another at R.M. Palmer Company’s factory, Chief Holben said at a news conference on Friday. The cause of the explosion was under investigation, he said.
The chocolate factory is just west of the Schuylkill and one block from Penn Avenue, a busy thoroughfare lined with cafes, ice cream shops and restaurants in West Reading, a borough of about 4,500 people that is about 60 miles northwest of Philadelphia.
A two-story factory building was flattened in the explosion, and on Saturday an excavator moved through mounds of damaged wood and warped metal where it once stood.
Frankie Gonzalez, 40, stood on a hillside overlooking the damage on Saturday afternoon, waiting for an update on his sister, Diana Cedeno, 45, a factory worker who has been missing since the explosion.
Mr. Gonzalez said that his family had waited at the hospital all night, unsure if Ms. Cedeno was even there. He said that Ms. Cedeno, who is married and has a 25-year-old son and a 20-year-old daughter, packaged candy at the factory.
Mr. Gonzalez said other workers had told him that before the explosion, they had been warning each other that they smelled natural gas and reported it to plant managers. He said that his son and a nephew had worked at the factory within the past year and had also told their supervisors they smelled gas.
Joseph Swope, a spokesman for UGI Utilities, a natural gas and electric company that serves the area, said that the company was cooperating in the investigation and that it was helping emergency workers on Saturday.
“The explosion damaged some of UGI’s facilities at the site, so gas was turned off to aid the firefighting efforts,” he said. “UGI did not receive a call prior to the incident for a gas odor or gas leak.”
Joshua Ramos, 30, said he was waiting to hear about the condition of his friend, Ziomaru Ivette, 28, who was hospitalized with injuries from the blast.
“They said she’s hanging in there,” Mr. Ramos said. “I hope she makes it. It’s heartbreaking.”
On Saturday, state and local officials reported different death tolls from the explosion.
The Pennsylvania Emergency Management Agency said on Saturday morning that five people had died and six others were missing. Officials in West Reading disputed those numbers and said on Saturday night that three people had died.
At least 10 people had been admitted to Reading Hospital, a spokeswoman, Jessica Bezler, said in an email on Saturday. She said two of the patients had been transferred, two had been admitted in fair condition and the others were discharged.
The explosion sent a column of debris, flames and dust shooting into the air, as shown in a video that was captured by weather cameras and that Eddie Kadhim, a reporter for Fox 29 News in Philadelphia, shared on Twitter.
“The explosion was so big that it moved that building four feet forward,” Mayor Samantha Kaag, who is also a firefighter, said at the news conference on Friday after she responded to the scene.
In an interview, Ms. Kaag said she had felt the explosion at her house, four or five blocks from the factory.
“I didn’t hear a boom,” she said. “I just felt it shake my house.”
R.M. Palmer was founded in 1948 and employs around 850 people, according to its website. It is known for making seasonal chocolates, including hollow milk chocolate bunnies for Easter.
Philip Wert, the vice president for the West Reading Borough Council, said at a news conference on Saturday that R.M. Palmer had been a “community partner” for decades.