A group of heavily armed gunmen stormed Pakistan's biggest airport on Sunday and at least 26 people were killed in a night-long battle at one of the country's most high-profile targets.

The assault on Jinnah International Airport in Karachi, Pakistan's sprawling commercial hub of 18 million people, took place as Prime Minister Nawaz Sharif's government tries to engage Taliban militants in talks to end years of fighting.

The attack began just before midnight when 10 gunmen wearing military uniforms shot their way into the airport.

Gun battles went on for five hours and television pictures showed fire raging as ambulances ferried casualties away. By dawn on Monday, the army said the airport had been secured.

"Ten militants aged between 20 and 25 have been killed by security forces," said a spokesman for the paramilitary Rangers force. "A large cache of arms and ammunition has been recovered from the militants."

Pakistan's paramilitary force said that the attackers were ethnic Uzbeks. Pakistani officials often blame foreign militants holed up in lawless areas on the Afghan border for staging attacks alongside the Pakistani Taliban around the country.

"Three militants blew themselves up and seven were killed by security forces," Rizwan Akhtar, the regional head of the paramilitary Rangers, said in televised remarks. "The militants appear to be Uzbek."

Officials said no aircraft had been damaged.

There was no immediate claim of responsibility, but Pakistani Taliban militants, allied with but separate from the Afghan Taliban, are battling to overthrow the Pakistani state and impose their hardline vision of Islamist rule.

Earlier, officials said all flights had been diverted.

Peace talks between the government and the Pakistani Taliban have failed in recent months, dampening hopes of reaching a negotiated settlement with the insurgency, which continues attacks against government and security targets. - Reuters