Two men have been stabbed to death after they tried to intervene when a man yelled racial slurs at two Muslim women on a light-rail train in Portland, Oregon, US police said.

A third train passenger, who also tried to stop the bullying, was badly wounded and taken to hospital, The Oregonian newspaper reported on Friday.

The suspect, 35-year-old Jeremy Joseph Christian of Portland, was arrested shortly after he left the train, police said.

Christian was booked into jail on two counts of aggravated murder and additional charges of attempted murder, intimidation in the second degree and being a felon in possession of a restricted weapon, police said. He was ordered held without bail.

Before the stabbing, the assailant was ranting on many topics, using "hate speech or biased language", and then turned his focus on the women, police spokesman Pete Simpson said.

"In the midst of his ranting and raving, some people approached him and appeared to try to intervene with his behaviour and some of the people that he was yelling at," Simpson told The Oregonian. "They were attacked viciously."

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One person was dead at the scene and another died at a hospital, Simpson said. The third person was taken to a hospital with non-life threatening injuries.

It was not clear why the man was yelling, Simpson said.

"He was talking about a lot of different things, not just specifically anti-Muslim," Simpson said.

The attack happened on a MAX train as it headed east. A train remained stopped on the tracks at a transit centre which was closed while police investigated.

Evelin Hernandez, a 38-year-old resident of Clackamas, Oregon, told the newspaper she was on the train when the man began making racist remarks to the women. A group of men tried to quieten him and he stabbed them, she said.

Simpson said the women understandably left the scene before police were able to talk with them but that they would like to hear from them to help fill in what happened.

"It's horrific," Simpson said. "There's no other word to describe what happened today."

The Council on American-Islamic Relations, America's largest civil rights and advocacy group, condemned the "horrific hate crime" and urged US President Donald Trump to renounce acts of racial violence targeting Muslims in the country.

"President Trump must speak out personally against the rising tide of Islamophobia and other forms of bigotry and racism in our nation that he has provoked through his numerous statements, policies and appointments that have negatively impacted minority communities," said Nihad Awad, CAIR's national executive director.

During his election campaign, Trump called for a total ban on all Muslims entering the US.

Since becoming president, he has issued executive orders aimed at limiting the movement of nationals of certain majority-Muslim countries to the US.