The gunman was found dead. "I told his wife he died a hero - he went in to save lives", Dean said.
A law enforcement official told The Associated Press that authorities have identified the gunman.
The Los Angeles Times quoted a law enforcement official as saying that at least 30 shots were fired inside the bar.
Authorities urged the public to avoid the area. Each moment was captured by TV cameras and broadcast live on cable networks as Americans grappled with another mass shooting.
"He made it through Las Vegas, he came home". That, in turn, closely followed the series of pipe bombs mailed to critics of President Donald Trump.
Trump said Thursday on Twitter that he has been "fully briefed on the bad shooting".
"He gave his all ... he went in to save lives, to save other people", Dean said.
The gunman was dressed in a black trench coat and wearing glasses when he walked into the bar filled with people enjoying a night of line dancing.
"Firefighters and first responders are arriving on scene of a report of a shooting at an establishment in @CityofTO". He said he thought their injuries were minor, and that majority were likely injured as they escaped, some by breaking windows.
"Impossible to put any logic or sense to the senseless", Dean said during a news conference.
By the time they entered the bar again the gunfire had stopped.
Marc Brown, an ABC7 reporter, said that he has seen one dead body outside the venue which does not match the description of the suspect.
The gunman opened fire at around 11:20 p.m. (1:20 a.m. CT Thursday).
The shooting happened on college night. According to the bar's website, a "College Country" night was going on at the time of the shooting.
"He was a great man", Capt. Garo Kuredjian, the force's public Information officer, told "Good Morning America" Thursday.
When the shots started, some people smashed windows with chairs to escape, witnesses told CNN.
In addition to those who died, injured or wounded patrons were brought to hospitals or went to them on their own. Three men rush out carrying a bloodied fourth individual.
The descriptions of chaos inside the club were similar to those reported during the slaughter of 49 clubgoers at Pulse nightclub in Orlando in 2016.
He said the only weapon found in an initial sweep was a handgun.
"Within a split second, everybody yelled 'get down, ' " she said. "I ran to the nearest exit and tripped and fell on the way and people kept running on top of me". It's something I had been setting myself up for, and then after the event, it really went into overdrive.
"I can't tell you what the status of any of those that were shot is at this point", he said.
Sgt. Eric Buschow, of the Ventura County Sheriff's Office, said that "multiple fatalities" had been confirmed.
"I screamed to him, 'There's a shooter in there!' He was kind of in disbelief, then saw that I was serious". He said he had friends who hadn't been accounted for.
A victim of the shooting is wheeled away minutes after the gun rampage.
People at the bar fled from all exits, broke through windows and hid in the attic and bathrooms, the sheriff said.