Members of the US Secret Service rush to a car, after it hit a motorcade SUV, as US president Joe Biden was leaving his campaign headquarters in Wilmington, Delaware on Sunday. AFP

A car crashed into a vehicle attached to Joe Biden's motorcade on Sunday, with the security scare startling the US president as he left his campaign headquarters in Delaware.

After a loud bang caused by a sedan slamming into an SUV positioned in a nearby intersection about 40 metres (130 feet) from Biden, security personnel rushed the president into a waiting vehicle and he was whisked away from the building in downtown Wilmington.

"Both the president and first lady are fine," a White House official told the media reporter who witnessed the incident. Further questions were referred to the US Secret Service.

Pool reporters had gathered on the sidewalk outside the campaign offices — where the president and First Lady Jill Biden had had dinner with staff — and had just finished shouting questions to Biden from a distance when they heard the crash and saw him with a surprised expression on his face.

Agents sprang into action, cornering the silver car with Delaware license plates and drawing weapons on the driver, who held his hands up.

US President Joe Biden (centre) looks on after a car hit an SUV in the motorcade in Wilmington, Delaware. AFP

Reporters were then quickly rounded up by staff to join the motorcade as it departed the rain-drenched scene.

"They're evacuating, you guys gotta go," a staffer told reporters as security personnel secured the area.

Biden arrived safely at his family home without further incident.

Agence France-Presse