Dorset County Council said the rock fall on East Beach near West Bay appears to have happened in the early hours of Friday.
It follows other landslips earlier in the year caused by winter storms.
The Jurassic Coast World Heritage team urged visitors to pay heed to warning signs and avoid "putting yourself or others at risk" by venturing close to the bottom of cliffs.
Drone pictures taken by local photographer James Loveridge show debris from the sandstone cliff spread out on the beach below.
Sam Scriven, earth science manager for the Jurassic Coast World Heritage team, said the cliffs were being monitored.
"As ever, keep your wits about you, whether you are out walking, fossil hunting, having a picnic or taking selfies.
"Always stay away from top and bottom of cliffs. Landslides and rock falls can, and do, happen anytime. Never ignore a warning sign - they are there for your safety."
Bridport Harbour also posted a warning on Facebook.
It said: "These can happen at anytime and without warning. Stay a safe distance away from the bottom of the cliffs."

The firm's progress is seen as a good indicator of global trade, as shipping carries about nine tenths of the world's trade, and Maersk Line is the world's biggest container carrier.
Maersk will probably book $3.4bn in profit for 2015, it said.
The company's shares fell 6.5% in early trading.
Shipping companies were charging about $233 to move 20-foot containers from Asia to Northern Europe, a loss-making rate according to analysis by Reuters.
Maersk blamed the drop in earnings on slender container shipping margins. It makes about half its profit from running the Maersk Line.
"Maersk Line has been hit harder than expected by low capacity utilisation due to the low volume growth in the global container transportation market," Sydbank analyst Jacob Pedersen said.

David Davis said "some people" were exploiting practices "to delay and dispute the outcome" of the inquiry, which began in 2009.
The government said it was a matter for the independent inquiry.
It comes amid growing pressure on Sir John Chilcot to set a publication date.
The inquiry, which is looking at the reasons for the UK's involvement in the 2003 US-led invasion, held its last public hearing in 2011.
The war saw British troops remain in Iraq until 2009 and a total of 179 UK service personnel were killed in the conflict.
Sir John this week wrote to families of UK soldiers killed in Iraq saying he understood their "anguish" at delays, blaming the "Maxwellisation" process - where those criticised are given an opportunity to respond.
His response came after some bereaved families threatened legal action.
Mr Davis said: "What appears to be happening is that some people are using the Maxwellisation process to delay and dispute the outcome of Chilcot."
The purpose of the process, he said, was to give people notice that they were going to be criticised and give them time to prepare for it and correct any errors of fact.
He said it was not meant to be a "process of private dispute and debate between the inquiry and those being criticised in order to influence the conclusion of the inquiry".
Mr Davis told the Telegraph ministers should now act.
"Surely the reasonable action for the government to take now is to say 'there should be a limit in time and money on what can be spent on government lawyers to allow this inordinate delay to continue'," he said.
When the Chilcot inquiry was launched, Prime Minister Gordon Brown said it would take at least a year.
Sir John has faced criticism in recent weeks, with Prime Minister David Cameron expressing his frustration at the delays.
The government spokesman told the Telegraph: "This is an independent inquiry and as such Maxwellisation, publication and timing are a matter for Sir John."
A section of cliff has collapsed onto a beach on Dorset's Jurassic Coast.
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Maersk, the Danish shipping and oil firm, said it will probably make $600m (£389m) less profit than previously thought, as global demand dropped.
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The government should limit the amount of money spent on legal advice for politicians, officials and military figures as part of the Chilcot inquiry into the Iraq war, a Tory MP has said.