The Taliban are claiming to have taken over the presidential palace in Kabul, BBC reported.
President Ashraf Ghani left the country earlier on Sunday - but the exact situation at the palace is still unclear.
According to local journalist Bilal Sarwary who spoke to two Afghans involved in direct negotiations, part of the agreement was that Ghani would join the transition of power ceremony inside the palace - but instead he and his senior aides left the country.
"Palace employees were then reportedly told to leave and the palace was (left) empty," the aides said. The Taliban later told a global wire service that they had taken it over.
There has been no confirmation from government officials.
Two officials from the Taliban told the wire there would be no transitional government following their lighting sweep across Afghanistan that led back to the capital two decades after the group were overthrown by US-led forces.
Ghani's destination was uncertain: a senior Interior Ministry official said he had left for Tajikistan, while a Foreign Ministry official said his location was unknown and the Taliban said it was checking his whereabouts.
Some local social media users branded him a "coward" for leaving them in chaos.
Taliban fighters reached Kabul "from all sides", the senior Interior Ministry official told the wire and there were some reports of sporadic gunfire around the city.
BBC reported an NGO which runs a hospital in Kabul claims more than 40 people have arrived at their hospital - most coming from the Qarabagh area, where there has been fighting.
The tweet, which cannot be independently verified by the BBC, says 22 people have been treated in hospital and those with more minor injuries have been referred to other facilities.
More casualties were arriving, it added.
There are reports of gunfire at Kabul's airport, according to a security alert just issued by the US Embassy.
Officials have instructed US citizens in the area to take shelter, as "the security situation in Kabul is changing quickly".
The Taliban issued a statement under the "Islamic Emirate of Afghanistan" banner saying the group has now been permitted to enter Kabul.
The statement claimed that Afghan police and other relevant institutions abandoned their duties and that to "prevent theft, looting and crime", the group's forces have been allowed to enter the capital.
"The Taliban will secure areas abandoned by Afghan forces in Kabul," said the statement.
It sought to assure citizens that the forces will neither enter their homes, nor "bother them".