Residents were ordered to evacuate parts of an Illinois community on Friday after the mayor there said authorities found a bomb at a local ethanol- and alcohol-production plant.

The discovery reported at BioUrja Renewables in Peoria triggered a mandatory evacuation over a one-mile evacuation zone encompassing sections of that city as well as the adjacent municipality of East Peoria. Officials ultimately lifted the evacuation zone at about 1.25pm local time on Saturday – but only after making it clear there had genuinely been a bomb found and ruling out the presence of any other explosives.

“It is real – this is a real thing,” Peoria’s mayor, Rita Ali, initially said, according to local news outlet WMBD. “We know that is a real threat. We know it is a bomb.”

Peoria’s police chief, Brad Dixon, said at a news conference early on Saturday that explosives technicians had rendered the bomb in question safe.

But Dixon asked for the public’s patience as investigators searched BioUrja Renewals’ expansive facility for other explosive devices, as the Peoria news outlet WEEK reported.

“We don’t know if there are other devices,” Ali remarked.

Meanwhile, Ryan Presley of the FBI, who is in charge of the bureau’s field office about an hour away in Springfield, Illinois, said agents would pursue whoever was responsible “tirelessly” and “bring them to justice”.

No arrests had immediately been announced, with authorities saying updates would be provided as an investigation into the case continued.

At about 7.05pm local time on Friday, the Peoria police department had announced that officers were “actively investigating a reported bomb threat at BioUrja Renewables”. The agency then urged “anyone who lives or works within a one-mile radius of the facility to immediately evacuate their homes and businesses until further notice”.

The police’s statement said the evacuation notice had been “issued out of an abundance of caution while officers and emergency personnel investigate the threat”, which officials initially referred to as a suspicious package. The city offered the Manual Academy school as a temporary shelter, and police said anyone who needed assistance evacuating their home or business could call for help.

“Most streets in this area have been closed off,” police also said.

In separate statement, the municipal government of neighboring East Peoria acknowledged that the evacuation zone associated with the package at BioUrja Renewables extended into part of that city. That area remained in effect as of 9am local time on Saturday, East Peoria’s government said.

A hockey game and a dance-themed charity event scheduled for Saturday had all been delayed, as WEEK reported.

And at least the Saturday portion of a Comic Con event scheduled to last through Sunday had been canceled, organizers said.

“This is not a hoax,” the Illinois state senator Dave Koehler said during the early Saturday news conference. “This has gone beyond that … This is serious. This is serious.”

In the Saturday afternoon update, Peoria police said “state, federal, and local law enforcement had conducted an extensive search of the BioUrja facility [and] … found no other items of concern at this time”.

Police said the evacuation order implemented on Friday would no longer have effect, and any closed streets would be reopened.

“Residents are now free to return to their homes in the area that was affected by this order,” police added.

Law enforcement receive bomb threats and suspicious package calls not infrequently. Even though officials take those kinds of calls seriously as they investigate the claims, they often aren’t verified as credible or substantial.

Friday’s BioUrja Renewables case came amid a particularly chaotic day in the US marked by a nationwide Federal Aviation Administration-ordered nationwide ground stop at US airports that was in effect for about four hours, canceling or delaying more than 11,000 US flights.

The country’s nerves were also frayed by a tanker which struck a cruise ship docked on the Mississippi River in New Orleans on Friday afternoon. First responders had to rescue passengers from the river’s water after the cruise ship turned on its side, and there were more than 30 injuries reported. But none of those injuries were critical, and there were no fatalities reported in association with the crash.