A photo of Hillary Clinton, former secretary of state and presidential candidate, glancing at a newspaper headline about US Vice President Mike Pence using a private email account has gone viral on social media, with thousands of people commenting on it.

Pence and others involved in the Republican presidential campaign last year criticised Clinton's use of a private email server during her time as state secretary.

Clinton was on an aeroplane travelling from Boston to New York on Friday when a fellow passenger snapped a photo of her glancing down at Friday's USA Today newspaper front page headline "Pence used personal email in office".

Pence's use of an AOL email account was first reported by the Indianapolis Staron Thursday. It said Pence used the account, which was hacked last summer, at times to discuss sensitive matters and homeland security issues while he was governor of Indiana.

Pence denies double standards

Pence said on Friday he had complied with Indiana laws in his use of the email account. He had an outside attorney review his private email records and archive those related to state business.

He said there was "no comparison whatsoever" between his use of an AOL account that was hacked and Clinton's private server.

Pence accused Clinton of "having a private server, misusing classified information, destroying emails when they were requested by the Congress."

During the campaign, US President Donald Trump and Pence said Clinton's use of a private server broke the law and endangered national security. Trump's comments led his supporters to chant "Lock her up!" at rallies.

The state department's internal watchdog said Clinton's use of a private server broke department rules. The FBI reviewed her emails for classified material, but it found that no criminal charges were warranted.