At least 45 people were killed overnight in Pakistan's commercial hub of Karachi after a member of the dominant political party in the city was shot dead, police said on Tuesday.
Dozens of vehicles and shops were set on fire as security forces struggled to gain control of the city. Karachi residents stayed off the streets Tuesday in anticipation of more violence.
The latest unrest came after Raza Haider, a provincial lawmaker, was shot dead along with his bodyguard in a mosque in the Nazimabad area of the city while attending a funeral on Monday.
"Initial investigations suggest that there were more than two people who came on a motorcycle and they were probably backed by armed men in a car," said a police officer at the Nazimbad police station, according to the Pakistani newspaper Dawn.
As the bodies of Haider and his bodyguard were taken to hospitals, Karachi descended into chaos, Dawn reported.
Officials told The Associated Press that the total death toll by Tuesday morning was 45. Some 80 additional people had suffered gunshot wounds, hospital officials said.
Sindh province spokesman Jamil Soomro said at least 10 people were arrested, and police and Army Rangers were dispatched throughout the city to impose order.
However, gunfire could still be heard Tuesday morning and fires were still being set in some areas.
A furniture market was among the places set ablaze.
Schools and colleges in Karachi and other urban centers in the province were ordered to stay closed by the government Tuesday. Some officials blamed unspecified "invisible hands" for the violence.
"It is very sad, and we believe that it is the work of those forces who want to destabilize the elected government," Soomro said.
The unrest comes as Pakistan struggles to deal with the worst floods in living memory. Monsoon rains have affected more than 3 million people so far and claimed the lives of more than 1,400, a spokesman for the U.N. Children's Fund said on Tuesday.
Such violence has raised fears of instability in Karachi, and the flight of Taliban militants to the city after army offensives against their bases in Pakistan's northwest has also sounded alarm bells.
The southern city of more than 16 million has a history of political, ethnic and religious violence, and has long been a hide-out for al-Qaida and Taliban militants. Its stability is important for Pakistan because it is the country's main commercial hub.
It was a main target of al Qaida-linked militants after September 11, 2001 attacks on the United States, when Pakistan joined the U.S.-led campaign against militancy, and foreigners were attacked in the city several times.
Haider was a member of the Muttahida Qaumi Movement, the political party that runs the city and represents mainly descendants of migrants from India who settled in Pakistan when it was created in 1947. The MQM called for three days of mourning.
Karachi police chief Waseem Ahmed told Reuters the police has credible information that Haider's killing was carried out by a banned sectarian organization. He did not say which one.
Police officials also said that they found evidence suggesting that a banned organization had planned a suicide attack during Haider's funeral, scheduled for later on Tuesday.
The MQM's main nemesis is the Awami National Party, a secular nationalist party whose main power center is Pakistan's northwest and whose base is the ethnic Pashtun community.
Independent analysts say followers of all political parties in Karachi are heavily involved in criminal activities such as protection rackets and illegal land dealings.
In certain neighborhoods, armed men linked to political parties stand guard at checkpoints.