Royal Navy ship HMS Enterprise has arrived in Beirut to assist following an explosion which destroyed the port and buildings across the city.
The survey vessel will carry out work to establish the extent of the damage, following last Tuesday's incident which killed hundreds and injured thousands more.
She has also brought with her tents, cots and field kitchen systems.
Enterprise's arrival comes as Lebanon’s Prime Minister Hassan Diab announced he is stepping down in the wake of the explosion, a statement made moments after his entire cabinet resigned.
In a brief televised speech, Mr Diab said he is taking "a step back" so he can stand with the people and "fight the battle for change alongside them".
"I declare today the resignation of this government. May God protect Lebanon," he said, repeating the last phrase three times.
The entire Lebanese government has been under increasing pressure after several ministers quit or expressed their intention to step down in recent days.
Over the weekend, security forces clashed with protesters - firing tear gas in the process.
Defence Secretary Ben Wallace authorised the deployment of Enterprise to the Lebanese capital last week.
British Ambassador to Lebanon, Chris Rampling, said Navy ship is part of a "very significant logistical package" in Beirut.
"In particular that is focused on recovery of the port and there is also a whole other package of assistance that goes with that," he added.
In addition to destroying the country’s main port, the explosion also damaged large parts of the capital, with nearly 300,000 people being left homeless in the immediate aftermath.
Authorities cordoned off the port itself, where the blast left a crater 200m (650ft) across and shredded a large grain silo, emptying its contents into the rubble.
Estimates suggested about 85% of the country’s grain was stored there and there are fears of imminent food shortages.
The Ministry of Defence said at the time of the explosion the British military would "continue to work with the Lebanese government to help the people of Beirut recover".
"A small team of experts will deploy to the British Embassy in Beirut to help coordinate the UK response ahead of HMS Enterprise's deployment and a further package of support," the department added.
The blast is believed to have been triggered by a fire which then ignited a giant quantity of ammonium nitrate fertiliser which had been stored in the port for several years.