Houthi militias captured the provincial government headquarters in Aden on Sunday, pushing into new areas of the battleground southern city despite a Saudi-led air campaign, a local official said.

The rebel forces advanced during the night to reach the central district of Mualla where they took the local seat of government including the governor's office, said the official, who did not want to be named.

The advancing Houthis, allied with several army units that have defected, bombarded residential areas, setting fire to several buildings and damaging others, witnesses said.

Video purportedly of fighting earlier in Mualla district in Aden, #Yemen http://t.co/3R7IKTLeIR Heart breaking. — Iona Craig أيونا كريچ (@ionacraig) April 4, 2015

Residents reported casualties and said dozens of families had fled their homes in the port city, the heart of which sits on an extinct volcano jutting out into the sea.

Basma Qassim, a 20 year old sociology student, previously described to Middle East Eye the effect of the bombs in Aden.

"I saw this orange and red flare, then I heard a boom; it shook my house," she said, adding that the Houthis had embedded themselves in the city. "The problem is that the Houthis are situated in every area...They're hiding weapons in the basement of restaurants."

The Houthis advanced to near the port of Mualla, which is defended by militiamen of "popular committees" loyal to President Abd Rabbo Mansur Hadi, who has fled to neighbouring Saudi Arabia.

"Snipers, who took position on the roofs of provincial government buildings, targeted passersby and members of the popular committees," pro-Hadi fighter Khalid Bashaea told AFP.

At least 185 people are reported to have been killed in the fighting in Aden between supporters and opponents of the president.

One child dead one injured #Mualla #Aden #Yemen when Saleh/Houthi rocket hits fourth floor home Main Street area http://t.co/ozS6MLzd99 — Jane Novak (@JNovak_Yemen) April 4, 2015

The Houthis, who hail from the country's mountainous northern area, overran the capital Sanaa in September and launched a power takeover in February, prompting Hadi to take refuge in Aden.

He left for Saudi Arabia last month as the Houthis and allied army units loyal to ex-president Ali Abdullah Saleh approached Aden, among the last footholds of Hadi supporters.

The Houthis seized the hilltop presidential palace in Aden on Thursday but soon retreated after air strikes by the Saudi-led coalition, which has been bombarding Houthi positions around the country for the past 11 days.

The coalition has also airdropped weapons to fighters supporting Hadi in the southern city.