Protesters have taken to the streets in cities across the US, as well as other countries, to demonstrate against the airstrikes in Syria ordered by US President Donald Trump.

Protesters in New York City, Philadelphia and Washington, on Friday chanted slogans against Trump’s controversial order and showed their support for the Syrian people.

Activists in New York had signs denouncing the bombing, including placards that read "Bombing Syria doesn't protect people, it KILLS THEM" and "NO! In the name of humanity, we refused to accept a fascist America."

The demonstrators also expressed their resentment against Washington’s warmongering policy and said bombing Syria would create even more conflict, not resolution.

"It's only going to escalate the violence," Martin Jennings, a protester, told local media. "I'm really concerned about the future of the Syrian people."

Demonstrators protest US airstrikes against Syria in Los Angeles on April 7, 2017. (Photo by AFP)

Some protesters said they did not believe Syrian President Bashar al-Assad was behind Tuesday's suspected chemical attack and said intervention would only make things worse.

"Get out of Syria, stop interfering, and let the people of Syria decide for themselves," protester Greg Butterfield said.

At least two people were arrested in New York City while another four were rounded up in Jacksonville, Florida.

Anti-war demonstrations have been planned for 50 cities across the US for the weekend.

The US military launched 59 cruise missiles on the al-Shayrat airbase in Homs province in the early hours of Friday.

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Trump said the operation was in response to the chemical attack in Idlib province. The Syrian government has strongly denied responsibility for that attack.

A protester shakes his hand and chants during a Stop the War Coalition demonstration opposite Downing Street in London, England. (Photo by Daily Mail)

In London, the British anti-war campaign group Stop the War Coalition took to the streets of Westminster to protest the US airstrikes.

In a message posted to the group's Facebook page, the organization said, “The Stop the War Coalition​ condemn​s Donald Trump's decision to launch attacks against Syrian targets.”

“As well as ​deepening​ the tragedy of the Syrian people, ​this utterly​​ irresponsible act ​threatens to widen the war and lead the West into military confrontation with Russia.,” another message read.