At least 27 people, mostly foreigners, have been killed in an attack on a beach near two tourist hotels in the Tunisian resort town of Sousse, according to the interior ministry.
Officials say one gunman has been shot dead and another is being pursued.
Sousse is a popular tourist destination.
Tunisia has been on high alert since March when militants killed 22 people, mainly foreign tourists, in an attack on a museum in the capital Tunis.
The interior ministry told the BBC "a terrorist attack" was ongoing. Officials say six people have been injured in the attack.
Tunisia attacks: Live updates
The attack comes on the same day as:
A man is decapitated and several others injured at a factory in France
A deadly attack on a Shia mosque in Kuwait
A British man on holiday told the BBC that he heard the attack on a neighbouring hotel.
From his room, he saw a man with a pistol but did not know whether this was an attacker or a member of the security forces.
The attack happened at a beach near the Hotel Imperial Marhaba, officials said.