Azerbaijan said Sunday that the country's second-largest city Ganja was "under fire" from Armenian forces, as fighting intensified over the disputed Nagorno-Karabakh region.

In statements posted on its website, the defence ministry said Ganja, a city of more than 330,000 in western Azerbaijan, and several other civilian areas were under fire from rockets and shelling. 

Earlier, Azerbaijani forces shelled Stepanakert, the main city of the breakaway region of Nagorno-Karabakh, Armenian officials said as fighting entered a second week.

In Stepanakert, an AFP team on the ground heard the sound of sirens at around 9:30 am followed by several explosions. Power in the city was out on Sunday.

"Azerbaijani forces are shelling civilian targets in Stepanakert with rockets," Armenian defence ministry spokesman Artsrun Hovhannisyan told AFP.

Azerbaijani authorities for their part said that they had taken "retaliatory measures" after rocket fire by Armenian separatists from Stepanakert.

The defence ministry in Baku said Armenian armed forces were firing rockets at the towns of Terter and Horadiz in the Fizuli region from Stepanakert.

Baku and Yerevan have for decades been locked in a simmering conflict over the ethnic Armenian province that broke away from Azerbaijan in a bitterly fought war in the 1990s.

New fighting that erupted September 27 has been the heaviest in decades and has claimed more than 240 lives, including more than 30 civilians.

The fighting continued despite international calls for the neighbours to halt clashes and begin talks as fears grow that the fighting could expand into a multi-front war sucking in regional powers Turkey and Russia.

French President Emmanuel Macron has warned NATO member Turkey -- which backs Azerbaijan -- against the alleged deployment of militants from Syria to the Karabakh conflict.

Karabakh's declaration of independence from Azerbaijan sparked a war in the early 1990s that claimed 30,000 lives, but it is still not recognised as independent by any country, including Armenia.

Talks to resolve the conflict have largely stalled since a 1994 ceasefire agreement