LIVERMORE (CBS SF) — An In-N-Out Burger restaurant in Livermore has been closed after a number customers reported getting sick, the company said Wednesday.

The restaurant on 1881 N. Livermore Ave. was closed after members of a large travel group reported feeling ill after eating there, according to a statement from In-N-Out Burger Vice President of Operations Denny Warnick.

READ MORE: Evacuation Warnings Issued for San Mateo County Areas Burned by CZU Lightning Complex Fire

A sign on the front door of the closed Livermore In-N-Out Burger restaurant. (CBS)

“We were recently contacted by nine customers that complained of flu-like symptoms after dining at our Livermore location,” said Warnick. “In an abundance of caution, we voluntarily closed the store, undertook an investigation and notified the local health department in accordance with our safety protocols.”

READ MORE: Police Investigation of Shattered Vehicle Windows Temporarily Shuts Highway 17 Saturday

Warnick said the investigation did not turn up any indication there were any issues at the restaurant. “Nevertheless, we thoroughly cleaned and disinfected the entire facility and screened our staff of Associates,” said Warnick. “We are confident that our customers are safe to dine with us and will re-open once the health department completes their assessment.

Livermore Mayor John Marchand commended In-N-Out for its quick response. “This is I think very responsible for them to proactively choose to close the restaurant down while they go through and find out what the cause is,” said Marchand.

MORE NEWS: Russian River Rubber Dam Deflated Due to Impending Storm

The Environmental Health Department of Alameda County said it suspected a case of norovirus, but that had not been confirmed Wednesday afternoon.