UPDATE 1-Suspect arrested after downtown Chicago shooting that killed 2

(New throughout, adds details from news conference)

May 20 (Reuters) - Chicago police arrested the suspected gunman in a fatal shooting that escalated from an altercation between two groups of young people outside a fast food restaurant and spilled on to a nearby train line, authorities said on Friday.

At least two people died and seven were wounded after gunfire erupted on Thursday night outside a McDonald's near the city's Magnificent Mile shopping section, authorities said.

After opening fire, the gunman fled to a nearby train station with police officers in pursuit. The individual was apprehended and a gun was recovered, Chicago Police Superintendent David Brown told reporters on Friday.

A woman was electrocuted after falling on the rail line and is now in critical condition, the superintendent said.

"This is a gun crime crisis in our city and in our country,” Brown said. "We are awash in guns." Police have retrieved record numbers of illegal guns from Chicago streets for two years in a row, he added.

Authorities said an investigation was underway and more details about the victims would be made public once charges are filed against those believed to be responsible. The wounded were transported to local hospitals in "serious to critical conditions," the Chicago Sun-Times reported.

"When the fight first started, we were right next to them," Deonna Jackson, who witnessed the events, told the Sun-Times. "We had to run because I didn’t want anyone to swing on me."

After the shooting, Chicago Mayor Lori Lightfoot promised to take additional steps to address "long-standing concerns along that block."

Lightfoot earlier banned unaccompanied minors from the city's Millennium Park after 6 p.m. Thursday through Sunday following a deadly shooting there involving teenagers last weekend.

Like several other U.S. cities, Chicago has witnessed a surge of deadly violence since the beginning of the coronavirus pandemic in 2020. (Reporting by Maria Caspani; editing by John Stonestreet; Editing by David Gregorio)