Mr Sharif is a fierce critic of government corruption
Officials of Pakistani opposition leader Nawaz Sharif have been accused of stealing electricity as he addressed a night rally to denounce corruption.
Mr Sharif's Pakistan Muslim League-Nawaz party has been accused by various newspapers of siphoning off power to provide lighting for the Lahore rally.
They say that it was done by extensive use of illegal connections.
Mr Sharif - who was making a speech against corruption at the time - has denied being personally responsible.
A Pakistan Muslim League-Nawaz (PML-N) leader, Saad Rafique, told an emergency press conference that the power supply had been arranged by Lahore administration officials to ensure security of the precinct where the public meeting was held.
Shown on TV
Another PML-N official, Siddiqul Farooq, said that an inquiry would be held to find out who was responsible for the illegal power connection.
Power theft is commonplace in Pakistan
Senior officials of the Lahore Electric Supply Company (Lesco) have refrained from blaming the PML-N outright for the theft. They said that they would identify those responsible by Tuesday morning, but so far this has not happened.
Television footage showed that metal hooks had been illegally connected to live wires to secure the electricity supply for the rally.
The BBC's M Ilyas Khan in Islamabad says that the rally was covered by all TV channels and almost all of them ran the video footage of the illegal connections, locally called "kunda".
Our correspondent says that the allegations are likely to be embarrassing for Mr Sharif, who in his speech indirectly denounced President Asif Zardari for making illegal money and stashing it away in foreign bank accounts.
Mr Zardari has denied persistent accusations of corruption over the years.