A lockdown of the US Capitol has ended after a man carrying a protest sign killed himself.

The man shot himself on the west front of the Capitol building in Washington DC just after 1pm yesterday local time. No one else was hurt.

Capitol police chief Kim Dine said the man had a backpack and a rolling suitcase, triggering an hours-long lockdown, and a sign that said something about "social justice".

Robert Bishop of Annapolis, Maryland, said he was cycling near the steps of the Capitol when the suicide happened.

There were about 60 people in the area, some of whom witnessed the suicide, including a tearful girl and her mother, he said.

Mr Bishop said another witness told him and a police officer that the man who killed himself held up a protest sign about taxation just before pulling the trigger.

No one was allowed to leave or enter the Capitol or the visitors' centre during the lockdown on a busy day for tourists, and some streets around the area were closed.

After being allowed to leave the Capitol, Mr Bishop said he saw authorities taking clothes out of the man's suitcase.

During the lockdown, about a dozen police cars, black SUVs and an ambulance congregated at the bottom of the west steps of the Capitol, which overlooks the bustling National Mall.

Police appeared to take measurements as bomb squad members searched the area. Nearer the mall, visitors gathered around trying to figure out what was going on.

The lockdown came during Washington's annual Cherry Blossom Festival, which attracts thousands of tourists.

Congress has been on spring recess for two weeks and members will return to work tomorrow.

PA Media