Plumes of smoke billowed over a provincial Afghan capital Thursday as fighting raged between the Taliban and government forces for a second straight day.

The government flew hundreds of commandos into Qala-i-Naw, in the northwestern province of Badghis, the first provincial capital to face an all-out assault by the Taliban since the United States stepped up its troop withdrawal.

With the US pullout "90 percent complete", according to the Pentagon, the insurgents have launched a blistering campaign to capture new territory, and fears are mounting that Afghan forces will be stretched without vital American air support.

Video obtained by AFP showed thick smoke billowing over the city, and the sound of gunfire could be heard.

Badghis health official Abdul Latif Rostaee said at least 10 civilians had been taken to hospital since the fighting erupted.

"The Taliban have resumed their attacks from several directions with light and heavy weapons," Badghis Governor Hessamuddin Shams told AFP on Thursday.

"Our security forces are bravely fighting them and the enemy is being pushed back. They are fleeing. We will give a hard blow to the enemy."

On Wednesday, the Taliban briefly seized the police headquarters and the local office of the country's spy agency, but were later pushed back.

Qala-i-Naw resident Aziz Tawakoli said Taliban fighters were still roaming the city, however.

"You can see them going up and down the streets on their motorcycles," he said.

Tawakoli said many of the city's 75,000 people had fled their homes -- either to nearby districts or to neighbouring Herat province.

"The shops are closed and there is hardly anyone on the streets," he said, adding that helicopters and planes had bombed Taliban targets through the night.

Badghis provincial council member Zia Gul Habibi said the Taliban suffered casualties, but also surrounded the city.

"All districts are under their control... People are really in fear," she said. 

"All shops and government institutions are closed. There are still reports of sporadic fighting."

Women will not be able to work

Parisila Herawai, a rights activist in the city, expressed concern for the safety of women in particular.

"It is an emergency situation for all women, especially activists," she told AFP.

"If the Taliban plan to remain in the city, we will not be able to work."

As news of the assault spread on Wednesday, social media was flooded with videos of clashes -- with some showing armed Taliban fighters on motorbikes entering the city, as onlookers cheered.

Local officials said some security officers had surrendered to the Taliban, and the insurgents opened the gates of the city jail, freeing hundreds of prisoners.

Most had since been recaptured, officials said.

Overnight, the defence ministry rushed hundreds of commandos to the city to launch a "large scale operation", spokesman Fawad Aman said on Twitter.

The attack on Qala-i-Naw comes as the Taliban carry out a blistering campaign across the country but mostly in the north, capturing dozens of districts since early May.

The fighting appeared to be spreading in Herat, where officials acknowledged losing two districts to the insurgents.

Rights group Human Rights Watch said the insurgents were forcing people from their houses in northern areas that they had captured.

"The Taliban's retaliatory attacks against civilians deemed to have supported the government are an ominous warning about the risk of future atrocities," said HRW associate director Patricia Gossman.

"The Taliban leadership has the power to stop these abuses by their forces but haven't shown that they are willing to do so," she said.