The Cablevision building on Route 58 in Riverhead was evacuated Wednesday afternoon after the valve to a 2,000-pound propane tank was knocked off by a worker, causing a leak just before 1 p.m.
A neighboring McDonald’s was also cleared out while firefighters investigated, fire officials said.
A construction worker fixing windows on the Cablevision building accidentally knocked off the valve while using a skid steer loader, said Riverhead Fire Department Chief Kevin Brooks.
The propane leaked for about 20 minutes, so people were asked to leave the two buildings as a precaution, he said.
No injuries were reported.