Gunmen dressed as doctors stormed Afghanistan's largest military hospital on Wednesday, officials said, killing at least 30 people in a six-hour attack claimed by a Daesh-affiliated group as it makes inroads into the war-battered country.

Afghanistan's Defense Ministry says an attack on Sardar Daud Khan hospital in the capital has killed more than 30 people and injured 50 others, mostly patients, doctors and nurses.

A Daesh affiliate claimed Wednesday's attack on the hospital in Kabul's heavily guarded diplomatic quarter, which set off clashes that lasted for several hours with explosions and gunfire rattling Kabul's diplomatic district as dense clouds of smoke rose in the sky.

Gen. Dawlat Waziri, a Defense Ministry spokesman, says there were "more than 30 killed and more than 50 wounded" in the attack.

He says security forces have taken full control of the facility and that the fighting is over.

Medical staff hunkered down in the hospital wards posted desperate messages for help on social media, with local television footage showing some of them trapped on the ledge of a top floor window.

"Attackers are inside the hospital. Pray for us," a hospital staff member wrote on Facebook.

Hospital administrators told AFP three gunmen wearing white laboratory coats began spraying bullets after a suicide bomber on foot blew himself up at the backdoor entrance, sparking chaos inside the 400-bed facility.

"I saw one of the attackers, armed with an AK-47 and dressed as doctor, shooting at patients and guards on the third floor," hospital nurse Abdul Qadeer told AFP.

"They shot my friend but I managed to flee... I had to jump over the barbed wire to escape."

At least two other loud explosions -- including what the defense ministry called a car bomb in the hospital's parking lot -- were heard as Afghan special forces launched a clearance operation that lasted around six hours.

The assailants were gunned down after Afghan special forces landed on the roof of the hospital in a military helicopter.

'Criminal act'

Afghanistan's warring parties, including government forces, have repeatedly targeted medical facilities, decimating the country's fragile health system and preventing conflict-displaced civilians from accessing life saving care.

"This is a criminal act. Nothing can justify an attack on hospitals," Afghan Chief Executive Abdullah Abdullah said of the latest attack.

"We will never forgive these criminals. Unfortunately, this attack has resulted in some casualties."

The Turkish Foreign Ministry also issued a statement strongly condemning the heinous terrorist attack on the hospital "where people in need of care" were receiving treatment.

Wishing a speedy recovery to the wounded and extending condolences to the brotherly people of Afghanistan, the statement reiterated that "Turkey will continue its support to the Government of Afghanistan in its fight against terrorism and in its efforts for bringing peace and stability to Afghanistan."

Daesh terrorists claimed the attack via a verified Telegram account.

The more powerful Taliban said they were not behind the attack. The militant group, Afghanistan's largest, is known to distance itself from attacks on medical facilities or those that result in high civilian casualties.

The assault comes just a week after 16 people were killed in simultaneous Taliban suicide assaults on two security compounds in Kabul.

Dozens of others were wounded as a suicide car bomber struck an Afghan police precinct in western Kabul and a five-hour gun battle ensued after another attacker snuck in.

In the second attack, a suicide bomber blew himself up at the gates of an Afghan intelligence agency branch in eastern Kabul.

The carnage underscores rising insecurity in Afghanistan. The country is bracing for an intense fighting season in the spring as the government's repeated bids to launch peace negotiations with the Taliban have failed.

Afghan forces, already beset by record casualties, desertions and non-existent "ghost soldiers" on the payrolls, have been struggling to beat back insurgents since US-led NATO troops ended their combat mission in December 2014.

Kabul last month endorsed U.S. General John Nicholson's call for thousands of additional coalition troops in Afghanistan to fend off the militants before the spring offensive.

Extra troops were needed to end the stalemate in the war, Nicholson, the top U.S. commander in Afghanistan, told the U.S. Congress in what could be President Donald Trump's first major test of military strategy.