Investigators in Lebanon probing the deadly blast that ripped across Beirut are now focusing on possible negligence in the storage of tonnes of a highly explosive fertilizer in a waterfront warehouse, while the government ordered the house arrest of several port officials.

The cause of Tuesday’s explosion is not immediately clear, but officials link the blast to some 2,750 tonnes of confiscated ammonium nitrate that had been stored in a port warehouse at the port for six years.

The explosion sent shockwaves through the Lebanese capital, killing at least 135 people and injuring 5,000 more.

Officials said they expect the death toll to rise further as emergency workers dig through the rubble to search for survivors.

More than 300,000 people lost their homes, and the Governor of Beirut Marwan Abboud said losses from the blast are estimated to be between $10bn to $15bn.

Lebanon’s cabinet has declared a two-week state of emergency in the capital and handed control of security in the city to the military.