Theresa May says ministers are looking at how to help firms "particularly adversely affected" by controversial changes to business rates.
The PM acknowledged there were "particular concerns" as a result of the revaluation of premises, which comes into force on 1 April.
There has been a fierce campaign against the move, with claims some firms face "eye watering" rises.
The government says most companies' rates will fall or stay the same.
Mrs May was asked about the changes during Prime Minister's Questions by Green Party MP Caroline Lucas, who said the changes would "devastate" the economy in her Brighton Pavilion constituency.
The PM said it was "right" for rates to change to reflect changing property prices, saying the system was underpinned by fairness.
She added: "We also, though, want to support businesses and recognise that for some, business rates will go up when these revaluations take place.
"That's why we have put significant funding in place for transitional relief.
"But I recognise that there has been particular concern that there will be some small businesses that are particularly adversely affected by the result of this revaluation.
"That's why I've asked the chancellor and the communities secretary to make sure there is appropriate relief in those hardest cases."
Business rates explainedImage copyright Getty Images
- Business rates are a tax on non-residential property such as pubs, restaurants, warehouses, factories, shops and offices
- The amount businesses pay is based on how much annual rent could be charged on the premises, which is known as the rateable value
- This is combined with the "multiplier" - a figure set by the government each year - to determine the final bill
- The Westminster government's revaluation, the first since 2010, applies to premises in England
- Revaluations are also taking place in Scotland and Wales, and Northern Ireland carried out one in 2015
Businesses pay tax based on the rateable value of their property, including pubs, restaurants, warehouses, factories, shops and offices.
These values are being reassessed for the first time since 2010, meaning changes to the amount many firms will pay.
In the face of opposition from business groups and some Conservative MPs, the government has defended the reforms and said 2017-18 "will see the biggest ever cut in business rates" and "three-quarters of all businesses, right across the country, will see their rates either fall or stay the same".
Asked afterwards whether the PM was proposing new cash to mitigate the impact of the changes, Mrs May's spokesman said she wanted to ensure the transitional relief was going to the right areas.
Communities Secretary Sajid Javid is likely to face questions about the revaluation during a Commons debate on local government finance later.
Also during PMQs, Mrs May defended the government's record on the NHS during fiery exchanges with Jeremy Corbyn.
After the Labour leader said the government had left the NHS in a "state of emergency", the prime minister said his party would "bankrupt the economy" leaving no money to spend on it.
Mr Corbyn also returned to his previous claim that a "sweetheart" funding deal had been offered to Surrey Council.
Mrs May said this claim had been "destroyed" and told him to apologise.