Three men and a 15-year-old boy have been arrested and charged by Toronto police in connection with a drug and firearm investigation.

Police have not said how long the investigation took, or what triggered it, however they said that on Saturday, four individuals were arrested and charged with numerous drug and firearm-related offences.

During the arrest, a fully-loaded nine millimetre Taurus handgun with 11 rounds of ammunition in the magazine, as well as a quantity of drugs, were seized, police say.

Adriel Rodrigues, 22, of Toronto, is charged with 17 offences, including possession of a loaded firearm and trafficking a controlled substance.

Aaron Verghese, 21, of Burlington, is charged with 14 offences, including carrying a concealed weapon and trafficking a controlled substance.

Awais Khan, 25, of Toronto, is charged with 18 offences, including three counts of possession for the purpose of trafficking and four counts of possession of a firearm while prohibited by a court order.

Khan was also wanted on a Canada-wide parole warrant which was executed upon his arrest, police say.

A 15-year-old boy from Toronto is charged with 14 offences, including three counts of possession for the purpose of trafficking and possession of a weapon dangerous to the public peace.

He cannot be identified under the terms of the Youth Criminal Justice Act.

All four of the accused appeared in a Toronto court on Sunday morning for bail hearings.

Investigators are asking anyone with information about this investigation to contact police or Crime Stoppers anonymously.