A woman was shot dead outside the US Capitol in Washington after she tried to ram through security barriers at the White House, officials said.

Police chased the car from near the White House to the Capitol and the shots were fired when the woman tried to flee.

Police confirmed that a baby was rescued from the car and has been taken into protective custody.

Officials did not give any more details on the woman involved in the incident.

They said there was no apparent connection to terrorism and a police official said it appeared to be an isolated incident.

The incident began near the White House and ended near the US Capitol, where the US House of Representatives and Senate were in session.

Politicians were trying to find a solution to a budget impasse that partially shut down the US government this week.

Officials said a vehicle struck a security barrier at 15th and Pennsylvania Avenue, near the White House.

Police chased the vehicle to 2nd Street and Constitution Avenue, near the Capitol, where the shots were fired.

One witness said several police cars chased a black sedan at high speed toward the Capitol. 

He said the car stopped outside the Capitol and he heard gunshots. One police car hit a bollard and was damaged.

An injured policeman was taken from the shooting scene in a Medevac helicopter, police said.

Capitol Police Chief Kim Dine said he believed there was a child in the car with the suspect.

Just before Capitol Police sealed off the Capitol building, the Senate and House were in session.

On the Senate floor, Senator John McCain of Arizona was urging that President Barack Obama and a bipartisan group of senators launch negotiations to break the deadlock over government funding and a debt limit increase.

The House had just passed a bill to fund the National Guard and reservists who are not on active duty during the shutdown.

The Capitol police, who were deemed "essential" staff, were at work despite the shutdown but they are not being paid.

Senator Roger Wicker of Mississippi told MSNBC he heard sirens and saw police motorcycles go by and then heard four to six shots fired.

The lockdown order at the Capitol was called off after about an hour and security along Independence Avenue was eased shortly before 3pm (8pm Irish time).

Tourists were allowed back onto th eCapitol grounds.

President Obama was briefed on the incident, a White House official said, providing no further details.

The shooting rattled the US capital three weeks after a government contractor opened fire at the Washington Navy Yard, about 2.4km from the Capitol.

Aaron Alexis killed 12 people and wounded three others before he was shot dead by police.

In 1998, a gunman burst through a security checkpoint at the Capitol and killed two Capitol Police officers in an exchange of fire that sent tourists and other bystanders diving for cover.

The suspect, Russell Eugene Weston Jr, was not charged with a crime because of apparent mental instability.