A number of British nationals are believed to be among those caught up in the aftermath of the huge blast that rocked the Lebanese capital of Beirut on Tuesday.
The explosion killed at least 100 people and injured more than 4,000 others, while more than 100 people are believed to be missing.
Boris Johnson said the UK government is "ready to provide support in any way we can", while the Foreign Office said it is "monitoring the situation closely".
Lebanon president Michel Aoun said the blast was caused by 2,750 tonnes of ammonium nitrate being stored unsafely in a warehouse.
According to a report that was shared following the explosion, the ammonium nitrate was on board a vessel that entered the Beirut port in September 2013 before being moved into warehouses the following month – where it has remained ever since.
The blast destroyed numerous apartment buildings, potentially leaving large numbers of people homeless at a time when many Lebanese have lost their jobs and seen their savings evaporate because of a currency crisis.
Estimates suggest some 85% of the country's grain was stored at the now-destroyed silos.
Lebanon's state-run National News Agency quoted the Raoul Nehme, the minister of economy and trade, as saying all the wheat stored at the facility had been "contaminated" and could not be used.
The tiny Mediterranean nation's economic crisis is rooted in decades of systemic corruption and poor governance by the political class that has ruled the country since the end of the civil war.
Lebanese citizens have held mass protests calling for sweeping political change since last autumn but few of their demands have been met as the economic situation has steadily worsened.
The coronavirus crisis – which has so far seen 65 deaths out of over 5,000 cases in Lebanon – added to the country’s woes, piling pressure on hospitals, where medical supplies reached critical levels.
Britons in Beirut
UK schools minister Nick Gibb that all embassy staff based in Beirut are accounted for, but that some have suffered "non-life-threatening injuries”.
In a tweet on Tuesday evening, Boris Johnson said the UK is ready to provide support in any way we can, including to those British nationals affected”.
A spokesman for the Foreign Office said: "All embassy staff are accounted for. A small number have sustained non-life-threatening injuries and, where necessary, are receiving medical attention.
"It is a fast-moving situation and we are monitoring the situation closely. We stand ready to offer consular support to British nationals affected.”
Cause of blast investigated
Abbas Ibrahim, chief of Lebanese General Security, said the blast might have been caused by the ammonium nitrate stored at the port but Donald Trump said US military generals had told him they "seem to feel" the explosion was the result of a "terrible attack" most likely caused by a bomb.
"It would seem like it, based on the explosion," the US president told reporters in Washington.
But schools minister Gibb said the president was "premature to speculate”.
"The Lebanese government have announced that they are conducting an inquiry and we are ready to help support the Lebanese government with any technical support that they need, but this is a tragedy and the Lebanese authorities are, of course, investigating the cause of that tragedy and I think before we have the results of that inquiry, I think it is premature to speculate," he told Sky News.