Authorities are searching for several missing people after firefighters and lifeguards helped rescue 13 immigrants believed to have been dropped into the water during a "dump and run" smuggling operation entering California from Mexico.

US Border Patrol and Coast Guard officers are searching for what police believe is a panga boat, a small fishing vessel often used to bring people into the US on coastal waterways, after as many as 16 people were left in the water off the coast of Del Mar.

Encinitas Fire Chief Mike Stein called the tactic a "dump and run", where a boat carrying immigrants from the other side of the US-Mexico border avoids heading to the shore and immediately heads back south.

The San Diego County Sheriff's Department said deputies first responded to calls for help around 4.30am on Friday before search and rescue teams were dispatched to coastal waters near Del Mar, roughly 30 miles from the US-Mexico border.

Rescuers, including an off-duty lifeguard, helped bring 11 people to the shore by 7am while officials searched the area by boat and helicopter. Two others were found hiding on a nearby beach.

'Dangerous' overcrowding of migrants in US border facilities







6 show all 'Dangerous' overcrowding of migrants in US border facilities









1/6 Photos of detained migrants crowded into cells at the US border - with one holding up a sign reading simply "help" - have been released as part of a new report warning of "dangerous" overcrowding. The memo was sent to the Department of Homeland Security by its Inspector General, containing photos taken at border facilities in the Rio Grande Valley over a week in June DHS/OIG

2/6 Eighty-eight adult males held in a cell with a maximum capacity of 41, some signalling prolonged detention to OIG Staff on June 12 DHS/OIG

3/6 Overcrowding of families observed by OIG on June 11, at a border patrol facility in Weslaco, Texas DHS/OIG

4/6 Migrant families overcrowding a border patrol facility on June 11 in McAllen, Texas DHS/OIG

5/6 Fifty-one adult females held in a cell designated for male juveniles with a capacity for 40 at Border Patrol’s Fort Brown Station DHS/OIG

6/6 Migrant families overcrowding a border patrol facility on June 11 in McAllen, Texas DHS/OIG

Solana Beach Fire Department Chief Robbie Ford said rescue crews are still searching for three others, though it's unclear whether they made it to shore or remain at sea. A lifeboat was found near the shore.

Chief Stein said most of the rescued people were suffering from mild hypothermia when they were brought to shore.

Border Patrol officers interviewed the migrants after they received care, according to authorities.

Officials did not release the nationality and ages of people in custody, but Border Patrol officers said that of the 13 people who were rescued eight were men and five were women.

Border Patrol agent Kurtis Kantura said the panga boat operators "care little for human life and will do anything they can to make a dollar".

The agency has participated in more than 900 search and rescue operations so far this year, following several high-profile water rescues of groups of immigrants entering the US from Mexico over the last several years.

Law enforcement also has encountered several abandoned panga boats in recent months carrying drugs into the US.