On the convention's second day, the speech's warm tone was out of step with a Republican gathering that featured harsh rhetoric about Democratic challenger Joe Biden and sometimes apocalyptic warnings about the dangers of Democratic governance.

Trump's wife acknowledged the pain of the pandemic in sharp contrast to most other speakers, notably her husband, assailed by Democrats for his lack of solace during a US health crisis that has killed more than 178,000 people.

"I want to acknowledge the fact that since March, our lives have changed drastically," Melania Trump told a crowd in the White House Rose Garden, the president in the front row. "My deepest sympathy goes out to everyone who has lost a loved one."

"And my prayers are with those who are ill or suffering. I know many people are anxious and some feel helpless. I want you to know: You're not alone."

With opinion polls showing Trump shedding support among college-educated women turned off by his combative style, Melania Trump and other women featured on Tuesday appeared to be trying to sway the critical voting bloc ahead of the November 3 presidential election.

The first lady reflected on the racial unrest that has swept the country in the months since the death in May of a black man, George Floyd, under the knee of a white policeman in Minnesota. Protests flared anew this week after a black man was shot and left paralysed by police in Wisconsin.

"I urge people to come together in a civil manner so we can work and live up to our standard American ideals," she said.

"I also ask people to stop the violence and looting being done in the name of justice and never make assumptions based on the colour of a person's skin."

The speech by Melania Trump, whose 2016 convention address was marred by plagiarism of lines from a 2008 Michelle Obama speech, capped a day when Republicans sought to reshape the narrative around the economy by largely ignoring millions of jobs lost to the coronavirus pandemic.

Trump, 74, still scores well in opinion polls on the economy, even as approval of his handling of the pandemic and other issues has plunged.

An array of officials and everyday Americans cited Trump's efforts to loosen economic regulations, put "America First" in trade deals and preserve religious freedom as reasons to back him against Biden, 77, Barack Obama's former vice president.

In an appeal to black voters, many of whom have been alienated by his sometimes divisive rhetoric, Trump in a video pardoned a convicted Nevada bank robber, Jon Ponder, a black man who has become an advocate for other inmates.

US Secretary of State Mike Pompeo, speaking from Jerusalem, praised a recent deal to normalise relations between Israel and the United Arab Emirates.

Pompeo, believed to be weighing a 2024 run for the White House, highlighted the 2018 move of the US Embassy to Jerusalem, which was popular with American evangelicals - a critical part of Trump's core support.

Melania Trump's remarks and the speech by Pompeo were criticised by Democrats who questioned the propriety of using the presidential residence for political purposes and of Pompeo making a political speech during a diplomatic trip to Israel.

Australian Associated Press