Former US Democratic Senator John Kerry on Monday formally started his first day at the State Department as the country's 68th secretary of state.

After entering the State Department's lobby, Kerry was greeted by loud cheers from the US foreign service staff.

"This is a remarkable place," he addressed his colleagues at the department. "I want to thank President Obama for his trust in me to take on this awesome task."

"I'm here today to ask you on behalf of the country, I need your help. President Obama needs your help to help us to do everything we can to strengthen our nation and to carry those ideals out into the world," Kerry said.

A son of a diplomat, Kerry was nominated by US President Barack Obama on December 21 as the next US secretary of state. He was sworn in on Friday.

Kerry launched a bid for the White House in 2004 but lost to then incumbent George W. Bush by a margin of 34 electoral votes.