(AFP) - Three police officers and a private security guard were killed by a lone gunman in a shooting spree near the French embassy in Tanzania's economic hub of Dar es Salaam on Wednesday, police said.

Head of police operations Liberatus Sabas told reporters that the motive of the gunman, who was shot dead at the scene by a police sniper, was not yet known.

"It's too early to conclude that this is terrorism as we still investigate the motives," he said. "Residents should remain calm as we investigate the matter."

He said that in addition to the four dead, six other people were injured in the incident in a usually calm seaside area of Dar es Salaam that houses a number of embassies.

Footage aired on local media showed a man in a checked shirt and white Islamic cap armed with an assault rifle roaming the street near a city bus.

He was later seen being shot and falling to the ground close to the entrance of the French embassy.

"The man appeared like a sheikh with a white cap. He passed near me without greeting and when I greeted him he did not reply. He was sweating. After a short while, we heard firing," said one witness who declined to be named.

President Samia Suluhu Hassan sent her condolences over the killings and called for police to conduct a thorough investigation.

US ambassador to Tanzania Donald J. Wright also sent his condolences over the "senseless attack", tweeting his "deepest thanks to the brave law enforcement personnel who brought an end to the rampage".

Jihadist monitoring group SITE reported later Wednesday that an outlet linked to the Islamic State (IS) group mentioned an "attack on the French embassy" in Dar es Salaam by a Somali man.

The French foreign ministry declined to comment when contacted by AFP.

The incident took place shortly after Hassan had hosted a meeting in Dar es Salaam of senior police officers, where police chief Simon Sirro said that crime had gone down in the year to June.

The opposition Alliance for Change and Transparency opposition party called for the security services to fully investigate the shooting.

"As the public, we need to know whether it was a lone event or one of greater security implications for our nation," party leader Zitto Kabwe posted on Twitter.

The US embassy in Tanzania had issued an alert as the incident was ongoing, telling its citizens to avoid the area.

© Agence France-Presse