(AFP) - A man armed with a shotgun and smoke grenades burst into a newspaper office in the US city of Annapolis on Thursday, killing five employees in what police described as a "targeted attack."

Officials said the shooting at the Capital Gazette was carried out by a white adult male resident of Maryland state who was being questioned in custody.

A reporter for the daily, which has roots dating back to the eighteenth century, tweeted a chilling account of how the "gunman shot through the glass door to the office and opened fire on multiple employees."

"There is nothing more terrifying than hearing multiple people get shot while you're under your desk and then hear the gunman reload," crime reporter Phil Davis said.

There were five fatalities and two superficial injuries, the acting police chief of Anne Arundel county, Bill Krampf, told journalists in Maryland's capital.

He identified the dead as four journalists -- Gerald Fischman, Rob Hiaasen, John McNamara and Wendi Winters -- and sales assistant Rebecca Smith.

"This was a targeted attack on the Capital Gazette," Krampf said.

The Baltimore Sun -- which owns the Capital Gazette -- identified the suspected shooter as Jarrod Ramos, who it said had a long-running dispute with the newspaper over a 2011 story "that covered a criminal harassment case against him."

Krampf said that police did not yet know the shooter's motive, but "we know that there were threats sent to the Gazette through social media."

"We're trying to confirm what account that was and we're trying to confirm who actually sent them," Krampf added.

- Still going to print -

Jimmy DeButts, a Capital Gazette journalist, tweeted that he was "devastated & heartbroken. Numb."

"I'm in no position to speak, just know @capgaznews reporters & editors give all they have every day. There are no 40 hour weeks, no big paydays - just a passion for telling stories from our community," DeButts wrote.

Chase Cook, a reporter at the newspaper, said the shooting would not stop The Capital -- the local print edition -- from going to press.

"We're putting out a paper tomorrow," vowed Cook as he typed grimly away in the shade of a car park, perched on the back of a pick-up truck.

"I don't know what else to do except this," he said. "We're just doing our job."

Gracie Rustin, a dental assistant who was in the middle of a procedure when the attack took place, heard "loud noises" but did not immediately realize it was a shooting.

Then police rushed in and "were like, 'Leave, leave, leave!'" Rustin told AFP.

Sean Robinson, who works for an insurance company, took shelter as far away as possible from the entrance and texted his wife to say, "Hey, this is going on. Just pray."

When he heard a sound at the door, he asked himself -- "friend or foe?"

It turned out to be a SWAT team, armed with assault rifles.

President Donald Trump, who has been at loggerheads with much of the media since taking office, tweeted a message of support.

"My thoughts and prayers are with the victims and their families. Thank you to all of the First Responders who are currently on the scene," he wrote.

- 'Attack on every American' -

"A violent attack on innocent journalists doing their job is an attack on every American," White House spokeswoman Sarah Sanders tweeted.

Several lawmakers also weighed in.

"My heart is with the families, friends and loved ones of the victims as we learn more about this terrible situation," Chris Van Hollen, the state's junior senator said. "We must unite to end the violence."

"The senseless attack on a Maryland newspaper today is sickening. God bless these journalists," House Speaker Paul Ryan tweeted.

A recent study found that Americans own 40 percent of the world's firearms despite accounting for only four percent of the global population.

Of the 857 million guns owned by civilians, 393 million are in the United States -- more than all of the firearms held by ordinary citizens in the other top 25 countries combined, according to the Small Arms Survey.

Advocates of tougher gun laws have stepped up their efforts in the wake of numerous school shootings this year, including the killing of 17 people at a Parkland, Florida high school in February and the killing of 10 people at a Texas high school in May.

So far the results have been relatively modest. Florida has raised the legal age to buy firearms from 18 to 21, while Texas Governor Greg Abbott focused on mental health and improving school safety in his list of recommendations following the Santa Fe shooting in the rural southeast of his state.

© Agence France-Presse