Four people were shot outside a baseball stadium crowded with thousands of spectators in the US capital on Saturday, causing the game to be abruptly halted as spectators were ushered out.

Police said four people had been shot but there was "no ongoing threat", without clarifying the condition of the gunshot victims.

Police tweeted officers were "responding to a shooting... in which two people where shot outside of Nationals Park," in the Navy Yard neighborhood of southern Washington, DC.

Shortly after, it tweeted that "two additional victims associated with this incident walked into area hospitals for treatment of gunshot wounds.

-This is currently an active investigation and it appears there is no ongoing threat at this time- it added.

Two AFP journalists who were at the game said some spectators had rushed for the exits after hearing the gunshots, while others remained in their seats at the announcer's initial urging.

Players rushed off the field and the game was halted after what sounded like a dozen or more shots were heard from outside the stadium.

The lights of multiple police cars lit up the street and sirens could be heard, as the crowd attending the game between the Washington Nationals and the San Diego Padres was then asked to leave the stadium.

Minutes after the incident, the Washington Nationals official account tweeted that "a shooting has been reported outside of the Third Base Gate at Nationals Park" and encouraged fans to exit the ballpark.