Hostages inside Karachi base after attack

Militants have attacked a Pakistani air base in Karachi, the country's largest city, police say.

Explosions and gunshots were heard as the attackers fought with troops at the Mehran naval aviation base. There are reports of at least four casualties.

Eyewitnesses say black smoke is billowing from the base.

The BBC's Shoaib Hasan in Karachi says that there are hostages inside the base.