A suicide bomber killed at least 25 people, many of them police, in Lahore on Monday, officials said, shattering a period of relative calm in Pakistan's second-largest city.

The blast wrought carnage near the Lahore Technology Park in the centre of the city, targeting police officials who were deployed to clear encroachments from the area, a police official said.

"The death toll we have now is 25 and over 30 are wounded," said Jam Sajjad Hussain, spokesman for the Rescue 1122 service.

Bomb blasts by militants are common in Pakistan, especially in tribal areas bordering Afghanistan, but attacks in Lahore have become less frequent in recent years.

Haider Ashraf, deputy inspector general of Punjab police, said the blast was a suicide attack and "police were the target".

Tehreek-e-Taliban Pakistan (TTP) claimed responsibility for the attack.

Interior Minister Chaudhry Nisar Ali Khan said the majority of those killed and wounded were police and warned the death toll could rise.

Prime Minister Nawaz Sharif condemned the blast in a statement and "directed for extending best possible medical treatment for the injured".

In early April, a suicide attack on an Army census team killed at least six people and wounded 18 in Lahore.