Five people were gunned down and two dozen others wounded in a pair of weekend mass shootings in the United States, the latest in a string of deadly gun attacks that have left lawmakers scrambling to tackle the crisis.

The shootings -- late Saturday in Philadelphia and early Sunday in Chattanooga, Tennessee -- further jolted a country facing a gun violence epidemic that has already claimed several thousand American lives this year and shows no signs of abating.

They come as polarized US senators find themselves under pressure to craft a measure that codifies at least basic, preliminary steps to help reduce the carnage.

In Philadelphia, two men and a woman were killed when multiple people opened fire on a crowd at a popular South Street nightlife area.

Philadelphia Police Commissioner Danielle Outlaw said one of the victims had gotten into a fight with another man, which could have been the cause of the shooting.

The two others were "innocent bystanders," she told reporters.

An eruption of violence in Chattanooga resulted in 14 people being shot, including two killed, while another person died and two more were injured after they were struck by vehicles fleeing the scene, police chief Celeste Murphy said, adding "several" victims remained in critical condition.

The pre-dawn incident occurred near a nightclub in a downtown section of the city of 180,000.

As of mid-Sunday no arrests had been made in either case, Murphy and Philadelphia media said.

Such gun violence has become almost commonplace in America, with more than a  half-dozen other shootings recorded over the weekend in which multiple people were killed, according to the Gun Violence Archive, which tracks shootings nationwide.

But the shock felt over recent mass shootings at a grocery store in Buffalo, New York and an elementary school in Uvalde, Texas, which saw 10 and 21 people gunned down respectively, have spurred ardent cries for action.

Democratic Senator Chris Murphy has been working with a bipartisan group of senators on reform measures -- a heavy lift with Republicans routinely rejecting most forms of gun control.

Senator Murphy said Sunday the group hoped to hammer together a legislative package that draws at least 10 Republican votes on top of expected support from nearly every Democrat.

"I think the possibility of success is better than ever before," he told CNN.

The emerging package, he said, would probably include "significant mental health investment, school safety money, and some modest but impactful changes in gun laws," including an expansion of background checks for gun buyers.

"Congress needs to do their jobs and pass commonsense regulation that will help stop this nonsense," an angry Chattanooga Mayor Tim Kelly told reporters.

He called for "mandatory background checks and prohibiting high-capacity magazines that allow shooters to hurt dozens of people without even having to reload."

'Guttural screaming'

Warmer weather tends to bring a spike in US violence, and in addition to the massacres in Texas and New York, recent weeks have seen mass shootings at a hospital in Oklahoma and a church in California.

Bystander Joe Smith, 23, told The Philadelphia Inquirer his mind had flashed to the recent incidents when he heard shots ring out Saturday.

"There was guttural screaming," he told the newspaper.

While Republicans have successfully blocked most efforts at gun control for years, some have recently spoken out for change.

In conservative, gun-loving Texas, more than 250 self-declared firearm enthusiasts, including donors to Republican Governor Greg Abbott, signed an open letter supporting efforts at bipartisan gun reform, the Dallas Morning News reported.

The letter, running as a full-page ad in the newspaper, endorsed an expansion of background checks, raising the age to buy guns to 21, and creating "red flag" laws intended to keep guns from people deemed to be at risk of violence.

US President Joe Biden last week called for new gun control legislation. On Sunday he renewed his call for restrictions on semi-automatic rifles.

"If we can't ban assault weapons as we should, we must at least raise the age to buy assault weapons to 21," he tweeted.

A CBS News/YouGov poll published Sunday shows 62 percent of Americans back a nationwide ban on semi-automatic rifles. Support is even higher for background checks on all gun buyers (81 percent) and "red flag" laws (72 percent).

US gun violence has killed 18,574 people so far in 2022, including nearly 10,300 suicides, according to the Gun Violence Archive.