"These destroyed drugs will never be injected into the arms of children on our streets or on the streets of Europe," Interior Minister Ali Ahmad Jalali said in a statement on Sunday.
"These destroyed drugs will never be sold to profit drug traffickers. And these destroyed drugs will not undermine the security of our country."
The largest drug stockpile was in the capital, Kabul, with 13 tonnes of opium, nine tonnes of hashish, two tonnes of heroin and six tonnes of other narcotics burned, the statement said.
Hundreds of plastic bags and sacks that officials said were filled with drugs were piled on top of each other on the outskirts of the city.
Workers doused the stash with petrol before lighting it up. Huge clouds of bluish smoke billowed into the sky and across the desert.
Seven stockpiles totalling about 32 tonnes of drugs were destroyed in other provinces, General Mohammed Daoud, deputy interior minister for counternarcotics, told reporters.
The event was held to mark the United Nations' International Day against Drug Abuse and Illicit Trafficking.
Afghanistan's government is under fire for not being tough enough on the burgeoning drug trade, which supplies nearly 90% of the world's opium.
The trade has sparked warnings that the country is fast becoming a "narco-state" less than four years after US-led forces ousted a Taliban government that had virtually eradicated the trade.
"These destroyed drugs will never be injected into the arms of children on our streets or on the streets of Europe"
Ali Ahmad Jalali,
Afghan interior minister
Last week, Counternarcotics Minister Habibullah Qaderi said that some provincial governors and police chiefs are suspected of involvement in the drug trade, but none are being investigated because of a "lack of evidence". He declined to name the officials.
The minister said many of the heads of the drug trafficking networks are also warlords, some of whom were commanders in the US-backed Afghan force that drove the Taliban from power in 2001.
President Hamid Karzai last month predicted a 20%-30% reduction this year in the amount of opium being grown, but Qaderi said strong rains after years of drought may lead to a bumper crop.
The United States, Britain and other countries are pouring hundreds of millions of dollars into an anti-drug campaign.
The cash is being used to train police units to destroy laboratories, arrest smugglers and destroy opium crops, as well as to fund projects to help farmers grow legal crops.
However, the drug traffickers have hit back at the threat to their business.
The drugs trade has burgeoned
since the Taliban fell in 2001
Late last month in two attacks on subsequent days, armed men killed 11 people associated with a US-sponsored project encouraging farmers not to grow poppies.
Qaderi said that this year 130 drug laboratories have been smashed, three opium markets raided, 130 tonnes of opium seized and 30 tonnes of chemicals used to process opium into heroin destroyed.
These figures compare with 135 tonnes last year and three tonnes in 2002.