T-R file photo An explosion rocked the north side of Marshalltown Sunday evening. No injuries were reported and the cause remains unknown.

Marshalltown Police and Fire departments received reports of an explosion on the north side of the city on Sunday.

Police received a call at 10:27 p.m. from a resident on the 800 block of N. Fifth Avenue. Another call came in from the 700 block of N. Fourth Avenue.

Fire marshal Josh Warnell said there was a reported smell of sulfur and haziness in the area.

Police officers and firefighters investigated the area but did not pinpoint where the sound came from.

“At the time we didn’t find anything suspicious,” said Police Captain Chris Jones. “We checked Central Iowa Machine Shop and everything appeared OK. We also checked the water pollution plant and everything was OK there.”

Jones said there is not cause for public concern at this point.

Warnell said the sulfur smell could be from the explosion of fireworks or bottle bomb — a homemade decoction of chemicals mixed in a bottle or jug that causes an expansion which explodes the container.

“They’re very unsafe,” he said of bottle bombs. “Sounds to me like someone messing around doing something they shouldn’t have.”

Typically bottle bombs do not leave behind physical evidence which can make them hard to discover, according to Warnell. If any sort of device were found it would prompt an investigation by the state fire marshal and the state’s explosives division.

“Homemade things like that are not going to have any signs,” Warness said. “A gas explosion is going to be completely different. If nothing can be found there’s not much we can do.”

This was not the first report of an explosion sound in Marshalltown in recent weeks, according to Jones. He said there have been two similar reports in the last four weeks.

“We’re still working with some other information we’ve had of other incidents like that happening on the other side of town,” he said. “We’re taking a look at all of the incidents that happened to see if there is any connection between them.”

Warnell urges the public to report incidents like this by calling 911 as soon as possible because a quicker response makes for a more effective investigation.

Contact Joe Fisher at 641-753-6611 or jfisher@timesrepublican.com